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Title: Practical Lithography
Author: Seymour, Alfred
Language:
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PRACTICAL LITHOGRAPHY
[Illustration: ALOIS SENEFELDER.
The Inventor of Lithography. Born 1781--Died 1834.]
PRACTICAL
LITHOGRAPHY
BY
ALFRED SEYMOUR
AUTHOR OF "MODERN PRINTING INKS AND COLOUR PRINTING" "RULE OF THUMB
IN THE WORKSHOP" "SOME WORK-A-DAY NOTIONS" ETC., ETC.
WITH FRONTISPIECE AND THIRTY-THREE ILLUSTRATIONS
LONDON
SCOTT, GREENWOOD & CO.
19 LUDGATE HILL, E.C.
NEW YORK
D. VAN NOSTRAND COMPANY
23 MURRAY STREET
1903
[_All Rights remain with Scott, Greenwood & Co._]
INTRODUCTION
"Alois Senefelder never benefited much by his discovery of the
elementary principles of lithography, but none of those to whom it has
given profitable occupation will remember without some feeling the
patient and persistent efforts of the struggling actor and dramatist
who, only after the greatest sacrifices and hardships, laid the germ of
this splendid development, and watched and guarded its growth." There is
one characteristic feature of the discovery of lithography for which
Senefelder ought to receive the fullest credit. Unlike other discoveries
of industrial and scientific value, there can be no doubt whatever as to
its origin. Senefelder's claim has never been disputed, yet "the payment
of a debt of gratitude to the fact is easily overlooked when the wheel
of history has made another turn."
It has been again and again suggested that the blighting influences of
Commercialism have robbed lithography of many of its traditional
features and a few, at least, of its best and most artistic qualities as
a reproductive art. This same commercial spirit, however, has inspired
and encouraged a charming variety of effect both in colour and design,
and lithography of to-day, in almost every form of its manifestation, is
infinitely more attractive and capable of considerably more expressive
power than could ever have been hoped for before commercial utility and
value demanded a full recognition. Pleasing and harmonious effects,
which are almost invariably sought after in lithography, need not be
inartistic; and it is quite possible for the technique of the
lithographic draughtsman to translate original work without a serious
depreciation of its pictorial and artistic value.
While expressing a sincere hope that this volume may be of considerable
assistance to his fellow-craftsmen, the writer wishes to emphasise the
fact that resourcefulness and intelligent application are faculties
which may be encouraged and amplified but cannot be imparted even by
volumes of text.
A mere formal acknowledgment of assistance cordially rendered by the
editors of the _British Printer_ and _The Caxton Magazine_ and _Press_,
Messrs. Penrose & Co., and other firms whose blocks are _primâ facie_
evidences of their interest, does not adequately express the
appreciation with which it has been accepted and made use of.
A. S.
LONDON, _December 1903_.
CONTENTS
PAGE
INTRODUCTION v
LIST OF ILLUSTRATIONS xi
CHAPTER I
ELEMENTARY DETAILS
Concerning Stones--Character and Texture--Some Simple
Elements--Preparation of Stones--Planing and Levelling--
Grinding Grained Stones--Descriptive Treatment--
American Method 1-7
CHAPTER II
LITHOGRAPHIC TRANSFER INKS
Various Forms--Distinguishing Features--Formulæ--Writing
Transfer Ink--Stone-to-stone Transfer Ink--Copperplate
Transfer Ink--A Modification 8-11
CHAPTER III
LITHOGRAPHIC TRANSFER PAPERS
Essential Features--Varnish Transfer Paper--Damp-stone
Transfer Paper--French Transparent Transfer Paper--
Copperplate Transfer Paper--An Alternative Recipe--
Granulated Papers--Photo-litho Transfer Paper 12-16
CHAPTER IV
COPPERPLATE TRANSFER PRINTING
The Copperplate Press--The Operation--Charging the
Engraved Plate--Cleaning-off and Polishing--Making the
Impression--Useful Notions 17-19
CHAPTER V
THE LITHOGRAPHIC PRESS
Mechanical Principles--Constructive Details--Scraper--
Tympan--Practical Suggestions--Elastic Bedding 20-23
CHAPTER VI
LITHOGRAPHIC PRESS WORK
Preparing the Design--Treatment of an Ink Drawing--Chalk
Drawings--Alterations--Value of Impressions--Offsets--The
Lithographic Hand-roller--Proving--Registration--General
Features--Transferring--A Commercial Necessity--
Arrangement--Choice of Paper--Transference to Stone--
Preparing the Forme 24-33
CHAPTER VII
MACHINE PRINTING
The Printing Machine--The Halligan--Some Mechanical
Phases--Speed--Pressure--Levelling the Stones--Cylinder
Brake--Inking Rollers--Damping 34-40
CHAPTER VIII
MACHINE PRINTING--_continued_
Register--Atmospheric Conditions--The Key--The Gripper--
Starting the Machine--Fixing the Stone--Strength of
Colour--Grit--Making Ready--Regulation of Speed 41-46
CHAPTER IX
LITHOGRAPHIC COLOUR PRINTING
A Commercial Value--Peculiar Features--Colour Sequence--
Controlling Elements--A Question of Register--Suitable
Paper 47-51
CHAPTER X
LITHOGRAPHIC COLOUR PRINTING--_continued_
Printing Inks--Varnish--Reducing Medium--Relative
Values--Some Useful Hints--Bronze Blue--Vermilion--Ink
Mixing--Ceramic Transfers--Colour Transparencies 52-56
CHAPTER XI
SUBSTITUTES FOR LITHOGRAPHIC STONES
Metal Plates--Preparation--Manipulation--Descriptive
Details--Machine Printing--The Printing Bed--Rotary
Printing Machine 57-66
CHAPTER XII
TIN-PLATE PRINTING
Its Evolution--Transfer and Direct Transfer Printing--
The Coated Paper--Reversed Designs--Sequence of
Printing--Printing Inks--Purity of Tone--Drying 67-71
CHAPTER XIII
TIN-PLATE PRINTING--_continued_
Direct Tin Printing--The Machine--Peculiarities of
Impression--Cylinder Covering--Colour Sequence--Printing
Inks--Drying Racks--Air-drying _versus_ Stoving 72-79
CHAPTER XIV
TIN-PLATE DECORATION
Suitable Designs--A Variety of Effects--Gold Lacquer--
Super-position of Colours--Embossed Effects--Embossing
Plates--Lacquers 80-83
CHAPTER XV
PHOTO-LITHOGRAPHY
Early Experiments--An Analysis--The Direct Process--
Transfer Process--Line and Half-tone--Some Difficulties--
A Natural Grain--Ink Photo-screen Effects--Essential
Features 84-88
CHAPTER XVI
PHOTO-LITHOGRAPHY--_continued_
The Copy--Gradations of Tone--"Scraper Boards"--Description
and Effect--Shading Mediums--Crayon Drawings--Half-tone
Copy 89-95
CHAPTER XVII
PHOTO-LITHOGRAPHY--_continued_
A Copying Table--Exposure--Illumination--Photo-litho
Transfers--The Paper--Printing--Developing--A Direct
Process 96-101
INDEX 102-104
ILLUSTRATIONS
PAGE
ALOIS SENEFELDER _Frontispiece_
STONE-PLANING MACHINE 4
STONE-POLISHING MACHINE 5
COPPERPLATE PRESS 17
HOT PLATE 18
LITHOGRAPHIC PRESS 21
DETAILS OF LITHOGRAPHIC PRESS 22
LITHOGRAPHIC HAND PRESS 23
LITHOGRAPHIC HAND ROLLER 28
REGISTER LINES 30
ARRANGEMENT OF TRANSFERS 32
TRANSFERRING BOARD 32
LITHOGRAPHIC PRINTING MACHINE 35
HALLIGAN MACHINE 36
PRESSURE MECHANISM 38
INKING ROLLERS 39
DAMPING ROLLERS 40
GRIPPER 42
TRIMMED EDGES 43
COUNTER SHAFTING 44
MOTOR DRIVING 45
PLATE-GRAINING MACHINE 59, 60
PLATE BED 62
ALUMINIUM ROTARY MACHINE 63
ALUMINIUM ROTARY SECTION 66
TIN-PLATE PRINTING MACHINE 73
TIN-PLATE RACKS 78, 79
METHOD OF STACKING PLATES 79
SCRAPER BOARD WORK 91
SCRAPER BOARD TEXTURES 93
PHOTOGRAPHIC COPYING BOARD 97
PRACTICAL LITHOGRAPHY
CHAPTER I
ELEMENTARY DETAILS
Concerning Stones--Character and Texture--Some Simple
Elements--Preparation of Stones--Planing and Levelling--
Grinding Grained Stones--Descriptive Treatment--American
Method.
There are a vast number of details in connection with lithography and
lithographic printing which are indisputably elementary in their
character. It would be impossible, however, to regard them as
non-essential, and a just appreciation of their value and influence must
of necessity enter into any comprehensive exposition of the craft.
_Stone as a printing medium._--The value of the Bavarian limestone was
one of those fortunate discoveries which tended to materialise
lithography as a graphic art, and may even be regarded as a fundamental
principle, the practical value of which is only equalled by its
far-reaching effects.
Other printing surfaces have been discovered and developed, with more or
less substantial results, yet without depreciating their merits, it will
be but a fair recognition to concede the premier position to the
Solenhofen and other limestones of a like nature.
The homogeneity and porosity of these stones render them peculiarly
suitable for lithographic purposes, and it undoubtedly reflects a vast
amount of credit upon Senefelder that even at the outset he should
select a medium so well adapted and in every way so eminently suitable
for graphic reproduction.
I have already, and almost inadvertently, indicated the peculiar value
of the Bavarian stone, for homogeneity and porosity of texture are
absolutely essential properties, and upon these is based almost every
theory which has assisted in the development of this craft. These
properties, in conjunction with a suitable greasy pigment, provide the
requisite materials for that cause and effect which require and compel
consideration.
The simple elements of lithography may be very briefly described, and in
this direction at least we must follow certain well-defined lines which
may be regarded as well-worn ruts, the consideration of which offers
little that is new.
A brief review of the theories of chemical and mechanical affinities is
best calculated to impress upon the mind the elementary principles of
the lithographer's art.
The penetrative power of a greasy pigment, together with the porous
nature of the litho-stone, may be regarded as the cause by which the
lithographer produces as an effect a design or impression which, to some
extent, enters into the texture of the stone--the homogeneity of which
checks any tendency to _spread_. This fatty matter may be applied in one
or two ways, either as a transfer from some other printing surface, or
as a direct drawing with pen, brush, or crayon.
The first question for consideration will be the initial preparation of
the litho-stones. These preparatory operations--which have for their
object the levelling, polishing, and cleaning of the stones--were at one
time entirely performed by hand labour, but are now accomplished with
much greater facility and in a more effective manner by machinery. The
importance of each individual operation will be more readily appreciated
when once its purpose is clearly understood. A litho-stone having a
_perfectly level_ surface is necessary in order to enable the printer to
secure a firm and uniform pressure over the whole design when printing
therefrom. A _smooth_, _polished_ surface will readily receive the
finest designs, and retain all their original characteristics. A _clean_
surface is an absolute necessity, _i.e._ a chemically clean surface free
from grease or any foreign matter which would be likely to enter into
the texture of the stone and by so doing injure any greasy drawing or
transfer which might be made thereon.
These are simple, elementary principles, and as such are probably
familiar to every reader, but the frequent result of familiarity is a
dangerous tendency to under-estimate the importance of everyday causes
and effects. If, therefore, such a reference as the above to common
details serves to convey some intelligent idea of their place and true
value, then no apology whatever will be necessary for their insertion in
this volume. It has already been stated that, in the preparation of
litho-stones, the superseding of hand labour by machinery has effected
considerable and important changes.
Several machines, all of more or less practical value, have been
introduced to the trade. One of the more recent developments, a
stone-planing machine, possesses many features of real merit (Fig. 1).
The stone is securely fixed on a perfectly true bed and passes slowly to
and fro beneath the blades of powerful cutting knives. These blades are
arranged in an inverted V-shape and locked in an oscillating framework.
By an automatic action they are almost imperceptibly lowered at each
traverse of the machine, when they lightly cut away the surface of the
stone until the old work is completely removed and a smooth level face
is assured. The chief objection to this type of machine is that in
course of time the knives become worn and slightly irregular, and it is
but reasonable to suppose that when a number of small stones have been
operated upon and immediately afterwards a full-sized stone is planed,
such irregularities will be very pronounced and detrimental.
[Illustration: FIG. 1.]
Many machines have been designed on the simple grinding principle, but
one type differs from its contemporaries and offers several distinct
advantages over them (Fig. 2).
This machine is constructed on hand-polishing lines, _i.e._ the
movements are to some extent mechanical arrangements of hand-polishing
principles. The size of stone makes no difference whatever, and the
results are in the main uniform and satisfactory. The inconveniently
sharp edges, such as are produced by the planing machine, are
unknown,--the wear and tear on the stone is perceptibly lessened, and
the power required to drive such a machine is not by any means a serious
matter.
When a planing machine does not enter into the operation, and grinding
by hand is therefore necessary, sharp, clean sand should be used as a
grinding medium. To secure some degree of uniformity in the grain, and
at the same time remove all the larger particles of grit, pass the sand
first through a fine sieve. The harder qualities of sand have, of
course, the greatest cutting power, and therefore are the most suitable
for this purpose.
[Illustration: FIG. 2.]
When hand-grinding is resorted to, a continuous elliptical motion of one
stone over the other with a slight twist from the wrist will prove most
effective.
To finish the grinding, and as far as possible remove the deeper sand
scratches, work off the sand in the form of a _sludge_. Unless this
operation is carefully and patiently performed, scratches of
considerable depth may appear on various parts of the stone's surface.
These, in the subsequent polishing, may offer a strong temptation to the
operator to work over one part of the stone more than another, so as to
effect the removal of such scratches with greater rapidity. The almost
certain result of this would be an uneven surface, which would in many
ways prove troublesome to the printer.
_The graining of stones._--This is a matter concerning the preparation
of stones which must not be overlooked. The introduction of shading
mediums and other contrivances of a similar character has considerably
minimised the importance of the grained stone, inasmuch as it cannot now
be regarded as an indispensable feature of lithography. It is, however,
still of inestimable value, and will probably always find a place and
purpose in the practice of lithography, despite its depreciation owing
to present-day limitations.
Recognising, then, the possibility of its retention, at least for some
time to come, as a suitable printing surface upon which the lithographic
draughtsman can work with undoubted facility of execution and effect, we
must perforce include a brief description of its preparation in this
chapter.
First of all, level the stone and to some extent polish it, after which
the graining may be proceeded with. A glass muller about 6 or 7 inches
in diameter makes an excellent "grainer." Failing this, a handy
substitute will be found in the form of a small litho-stone, hard in
texture, and with a smooth, level surface. Use as a graining medium
sharp, clean silver sand only, passing it carefully through a sieve
according to the size or depth of the grain required. Sprinkle a little
of this sand uniformly over the stone under treatment, together with a
few drops of clean water. With a continuous circular movement pass the
graining muller from end to end of the stone, exerting a firm and
uniform pressure. Repeat this operation again and again, adding sand
and water as required. Considerable time coupled with intelligent
application will be necessary to carry out this work successfully.
Should the sand become too much worn before its renewal the grain will
in proportion lose its "tooth" or sharpness. On the other hand lies the
danger of producing a grain which is too harsh or pronounced. Therefore
much depends upon the skill and judgment of the operator. A safe plan is
to ascertain the progress at any time when a satisfactory result might
be reasonably expected. The best way to accomplish this is by washing
from the face of the stone any accumulation of sand, and drying it, so
that a test can be made with the actual grade of crayon to be used in
the subsequent drawing. A powerful current of clean, cold water affords
the best means for removing every trace of sand from the finished stone,
and will leave it in a condition of almost complete readiness for the
draughtsman; a good drying is then all that is necessary. Good results
have been claimed for a method of graining which was introduced by the
Americans a few years ago. In this process the grain is produced by
sprinkling the surface of the stone with sand and rolling it with small
glass balls. These balls having a limited area in which to work exert a
continuous cutting power without any tendency to produce scratches. Some
mechanical arrangement is necessary to impart this continuous rolling
movement to the glass balls and to maintain a uniform speed. It is quite
easy to understand that with such a process, carried out under
favourable conditions, very fine results might be produced with great
rapidity.
CHAPTER II
LITHOGRAPHIC TRANSFER INKS
Various Forms--Distinguishing Features--Formulæ--Writing
Transfer Ink--Stone-to-stone Transfer Ink--Copperplate
Transfer Ink--A Modification.
Given a perfectly clean and smooth polished stone as described in the
previous chapter, the next important point is the composition of the
fatty matter wherewith a design or drawing is applied.
As already stated, the active principle in any suitable transfer medium
of this character is invariably the same, no matter what form its
composition takes. For applying with pen or brush it must possess
soluble properties, and of necessity be reduced to a liquid form. Such
soluble properties, however, must not interfere with its fatty
properties, these latter being essential features.
In crayon or _chalk_ drawing the composition must be employed in a
concrete form, as a crayon, the hardness and texture of which will be
controlled (1) by the character of the work to be carried out; (2) by
the character of surface to be operated upon.
Transfers from other printing surfaces can only be made when the
composition used is in the form of a pigment, and reduced to a
convenient working consistency.
These, then, comprise the varieties of transfer mediums which are likely
to be required in most phases of commercial lithography. Others are, of
course, employed for specific purposes and under peculiar conditions;
but these, again, are more or less modifications of existing formulæ,
prepared to meet particular requirements.
The ink used for transferring impressions from one printing surface to
another, _e.g._, the re-transferring of work from stone to stone, may
with a very slight alteration serve for type to stone transfer; but a
considerable departure must be effected to produce a satisfactory
photo-litho transfer ink, while a composition of a peculiarly
distinctive character will be requisite for the successful production of
transfers from copperplate engravings, as well as for a transfer ink for
writing and drawing on stone or transfer paper. This writing transfer
ink must be soluble in water, yet without becoming slimy; otherwise it
will not work freely with the pen or brush. It must also dry quickly,
and without any tendency to smear.
A plate transfer ink must neither melt nor drag when applied to the hot
plate. It must, of course, soften sufficiently to fill in the lines of
the engraving, and should so harden as it cools that it cannot easily be
dragged away during the cleaning and polishing operations. See Chap. IV.
page 19.
Each and all of the above inks must be excessively greasy and
penetrative, but without having the slightest tendency to spread
superficially. The ingredients and methods of preparation specified in
the succeeding paragraphs are not given as standard formulæ, but in
corroboration of statements made, and as practical illustrations of the
character and purpose of transfer inks and compositions generally.
_Transfer ink._--Writing transfer ink, for writing or drawing on stone
or transfer paper, may consist of equal quantities of:--
Castile soap,
Wax,
Tallow,
Shellac,
with the addition of carbon black or black printing ink as a colouring
matter. Another reliable formula is:--
Soap 4 parts
Tallow 3 parts
Wax 6 parts
Shellac 4 parts
Carbon black 1 parts
Whichever formula is adopted the method of preparation is the same
combination.
Free the soap from all moisture by drying, and thus facilitate its
combining with the other ingredients.
Melt the tallow and wax over a hot fire until they are thoroughly well
mixed. Add the dried soap a little at a time, so that it may become
thoroughly incorporated with the wax and tallow. Bring the mixture to
boiling-point, then remove it from the fire or stove and ignite the
fumes which will then be rising freely. Continue the burning process for
about fifteen minutes, then extinguish the flames by replacing the lid
of the pan. The shellac and black may be added while the composition is
cooling.
_Stone-to-stone re-transfer ink._--The ingredients of this ink consist
of:--
4 oz. Transfer ink.
4 oz. Litho black ink.
4 oz. Medium varnish.
1 oz. Canada balsam.
Melt the transfer ink over a slow fire and add the other ingredients
separately.
Canada balsam will not only add to the effectiveness of this ink, but it
will also improve its working qualities.
_Copperplate transfer ink._--Ingredients consist of:--
1 oz. Tallow.
3 oz. Bee's wax.
4 oz. Shellac.
2 oz. Soap.
4 oz. Bitumen.
1 oz. Canada balsam.
1 oz. Carbon black.
The method in this case differs somewhat from the preceding. First melt
the bitumen and then add the wax and soap in small pieces as before.
Burn this for fifteen minutes, and add the shellac, balsam, and black,
boiling the whole gently for forty minutes. Mould into squares or
sticks, and for convenience in handling cover these with tinfoil.
Should an extra powerful ink be required for shading or stippling films,
the stone-to-stone re-transfer ink can be reduced to a working
consistency with castor oil instead of varnish, and thus rendered
suitable for this purpose.
CHAPTER III
LITHOGRAPHIC TRANSFER PAPERS
Essential Features--Varnish Transfer Paper--Damp-stone
Transfer Paper--French Transparent Transfer Paper--
Copperplate Transfer Paper--An Alternative Recipe--
Granulated Papers--Photo-litho Transfer Paper.
Transfer papers are even more used than the transfer compositions
already described, and in greater variety, in consequence of which there
is a wide difference of opinion concerning their merits.
To a certain extent the specific value of any transfer paper must depend
upon local conditions. That which might be of the utmost value to one
printer would in all probability fail to meet the requirements of
another. With these also, as with the transfer inks, the main point is
to grasp the general principles involved. Adhering to these principles
enables any intelligent workman to adapt the transfers to his own
peculiar necessity. It is most important that lithographic transfer
paper should be absolutely impervious to the transfer composition or
ink, so that an impression of full strength can be conveyed to the
stone, leaving its greasy properties unimpaired. The paper therefore
must undergo special preparation, and here again the character of the
work and the conditions under which it is carried out are the chief
controlling elements. So much is this the case that many lithographic
printers prefer to make their own transfer paper, and find such a
procedure eminently satisfactory.
A good bank post double foolscap paper, about 26 lb., first thinly
coated with a solution of concentrated size and afterwards varnished
with a heavy coach body varnish, gives excellent results. When
transferring large work in which a number of printings are involved, and
where accuracy of register is a _sine quâ non_, the following mixture
may, if desired, be substituted for the coach body varnish:--
Best oak varnish 1 quart.
Turpentine 1/2 pint.
Boiled linseed oil 1/2 pint.
Paper thus prepared rarely stretches or becomes distorted to any
appreciable extent, and can be used with equally good results on either
cold or warm stones.
Its keeping qualities are, however, limited; it is therefore advisable
to utilise the transfer impressions with as little delay as possible.
This may be criticised as a somewhat primitive and old-fashioned
transfer paper; but of the many transfer papers now in use, none can
claim to be exactly new.
Another stone-to-stone transfer paper of the simplest possible character
can be made by coating a good writing paper with the following
composition. Soak 3 oz. of glue in 6 oz. of water for about 8 hours.
Reduce 1 lb. of starch to a thick, creamy paste by rubbing it down in a
little cold water and then adding boiling water until the required
consistency is obtained. Mix the starch and glue together, and add a
little gamboge or cochineal as colouring matter, so as to enable the
printer to see at a glance which is the coated side of the paper. Spread
this composition on the paper while it is still warm.
A transparent transfer paper with a soluble coating is frequently
desirable, and for certain purposes may be strongly recommended. A
French transfer paper meets such a requirement, and at the same time
possesses many other excellent qualities. It picks up a firm, clean
impression, and transfers every particle of it to the stone. It is also
transparent, and sufficiently adhesive to stick to a very slightly
damped stone under a light pressure.
A transfer paper which may be used as a base upon which to write or draw
a design for subsequent transference to stone, as well as for
stone-to-stone transferring, should be coated with a composition of a
gelatinous character, which will not be readily soluble in water.
Writing transfer ink is of course dissolved in water, and its effect on
a soft, soluble composition would be disastrous.
The following formula is suggestive as well as practical:--
Gelatine 4 oz.
Isinglass 6 oz.
Flake white 3 lb.
Gamboge 2 oz.
Make a strong size of the above by boiling the gelatine and isinglass
with a little water. Mix the gamboge and flake white with a little warm
water, and add the mixture to the gelatine solution. This composition
must be applied to the paper while still quite warm, as it forms into a
comparatively stiff jelly while cooling. This paper should be
transferred to warm stones.
Copperplate transfer paper is to some extent a development of the
variety just described; that is, if the conditions under which such
transfers are made will bear comparison with operations of an
essentially different character.
The composition used for coating copperplate transfer paper must possess
a somewhat heavy body, and for this reason plaster of paris enters into
its composition, which is as follows:--
Plaster of paris 2 lb.
Flake white 1 lb.
Flour 2 lb.
Fish glue 1/4 lb.
Alum 1 oz.
Soak the alum and glue from 8 to 10 hours, and then boil them until they
are dissolved. Make the flour into a smooth paste by the addition of a
little water, and mix it with the flake white. Mix the plaster of paris
with water, and stir continuously until it becomes incapable of setting.
Add the other ingredients, already mixed, and see that they become
thoroughly incorporated with the plaster of paris, after which coat the
paper twice with the mixture.
The following may be substituted for the above:--
Plaster of paris 2 lb.
Flour 2 lb.
Gelatine 4 oz.
A transfer paper with its surface granulated to represent a mechanical
stipple, or the texture of a grained stone, may be prepared in the
following manner. Take of:--
Starch 9 oz.
Parchment chippings 12 oz.
Flake white 14 oz.
Prepare the starch as previously described, and dissolve the isinglass
by boiling. Mix the flake white into a thin paste by the addition of
water. Warm the three ingredients, and mix the whole thoroughly. Coat a
fairly heavy printing paper twice with this composition, and when it is
thoroughly dry give it the required granulation by means of grained
stones or engraved plates. The grain thus imparted breaks up the drawing
into a series of minute dots. Paper of this description is most suitable
for pencil or crayon work. Its usefulness is obvious. It enables the
artist to use his chalks in the usual manner, without the inconvenience
of handling large stones. No graining of the stone is necessary, and the
grained effect can be confined to any portion of the design.
Photo-litho transfer paper is in every respect a specific article, the
coating of which consists of a gelatinous emulsion, which can be readily
sensitised, and upon which a photographic image can be developed.
Special preparation and manipulation are therefore necessary in
connection with its production, and these points will be fully dealt
with in a subsequent chapter.
One more variety of transfer paper should be mentioned, namely, the
diaphanic, which possesses excellent qualities for certain classes of
work. It is very transparent, and extremely useful in the tracing of key
formes, or for making facsimile drawings for immediate transference to
stone.
CHAPTER IV
COPPERPLATE TRANSFER PRINTING
The Copperplate Press--The Operation--Charging the Engraved
Plate--Cleaning-off and Polishing--Making the Impression--
Useful Notions.
Although copperplate printing may not now be so extensively practised as
in years gone by, it is not, so far as we can judge, very likely to be
superseded in the near future. It is still regarded as a necessary
adjunct to lithography, especially where the amount of commercial work
produced is of any moment.
From a purely mechanical point of view the construction of the
copperplate press (Fig. 3) is of an exceedingly simple character. Its
primary purpose is to produce a heavy and uniform pressure on the plate
during operation.
[Illustration: FIG. 3.]
After being charged with a special pigment and cleaned as hereafter
described, the plate is laid, face upwards, on the iron bed or table of
the press and in contact with the paper, and passed through between two
iron cylinders. These cylinders are so adjusted as to produce an
exceptionally heavy pressure. Such are the simple elements of a process
which, however, requires much closer investigation.
In its application to lithography the following are the only requisites
for copperplate transfer printing.
A stick of prepared transfer ink--whiting, free from grit--transfer
paper, and a plentiful supply of soft rags. Likewise, an iron plate with
a gas jet underneath (Fig. 4), a square of printer's blanket, and a damp
book consisting of twenty or thirty sheets of blotting or other
absorbent paper slightly and uniformly damped.
[Illustration: FIG. 4.]
A good copperplate transfer paper can be made according to the recipe
given in Chap. III., but unless a fairly large quantity is used the
commercial qualities will be found most economical.
Copperplate printing, in its application to lithography, is a simple
operation, but it requires extraordinary care for its successful
execution. The conditions under which lithographic transfers are made
from a copperplate engraving are vastly different from those which
control copperplate printing for ordinary purposes of reproduction.
The engraved plate is first well heated by means of the hot plate
already mentioned. The transfer ink is then _forced_ into the engraved
parts until every line is fully charged, the ink having been previously
enclosed in a double fold of soft rag.
During this part of the operation great care must be taken that the
transfer ink does not burn through overheating, as this would partially
destroy its greasy nature and leave it hard and brittle. The transfer
impression would suffer in consequence, and, though to all appearance
perfect on the paper, it would be weak and ineffective when applied to
the lithographic stone. Such an error of judgment is not at all unusual,
and should therefore be the more carefully guarded against. It
frequently occurs without the knowledge of the operator, owing, it may
be, to his over-anxiety to complete his work in as short a time as
possible.
The plate must now be cleaned, _i.e._ the surplus ink and scum must all
be removed. This may be done before the plate is quite cool, and after a
little experience it will be possible to accomplish the cleansing
process without in any way disturbing the ink in the lines of the
engraving. The rag used for cleaning must be tightly folded into the
form of a pad and kept free from creases. After final cleansing and
polishing with whiting the plate is ready for an impression. The
transfer paper requires damping until it is quite limp, when it is
brought into contact with the inked plate and subjected to a very heavy
pressure. The backing is a woollen blanket, preferably of fine texture;
this ensures perfect contact between the plate and the paper. The plate
is now very slightly warmed to dry the transfer paper, which is allowed
to peel off; this it does very readily if, after a little while, the
corners and edges are but slightly eased.
Oil of tar will effectually remove any accretions of copperplate
transfer ink which may have hardened in the lines of the engraving.
It may be useful also to know that it is possible to use a small
lithographic press in place of a copperplate press, assuming, of course,
that a sufficiently heavy and uniform pressure can be guaranteed. This
is not altogether an innovation, yet it is not a familiar notion.
CHAPTER V
THE LITHOGRAPHIC PRESS
Mechanical Principles--Constructive Details--Scraper--
Tympan--Practical Suggestions--Elastic Bedding.
It is not a little surprising to find that the mechanical principle of
the lithographic press in general use to-day is almost identical with
that which the pioneers of the craft employed so successfully. This is
an interesting fact which either reflects much credit upon the ingenuity
of the early lithographic printers or points to an unreasonable
conservatism on the part of the present-day craftsmen. A discussion of
this phase of the question would be of doubtful interest, for the
practical printer has long been accustomed to regard it simply as a
convenient appliance for the production of a heavy and readily
adjustable pressure.
A brief examination will prove to what extent these requirements are
fulfilled by the modern lithographic press (Fig. 5).
The simplicity of its construction suggests a first point for favourable
criticism. In fact, its general mechanical arrangements are so
exceedingly simple that the merest tyro might readily understand their
principles and purpose.
The adjustability of the pressure by means of the screw D (Fig. 8) is
both effective and necessary, owing to the constantly varying thickness
of the lithographic stones.
The pressure of the boxwood scraper B on the surface of the stone is
perfectly rigid, and yet, owing to the intervention of the tympan C, is
sufficiently elastic to ensure the closest possible contact. Figs. 6 and
7 show one or two constructive details by which the hand lever A and the
cam motion E bring up the cylinder F to the bottom of the carriage or
bed of the press, Fig. 8.
[Illustration: FIG. 5.]
It is in this position that the movement of the carriage gives the
necessary pressure required to pull an impression. The shaft H runs
across the press and operates a similar cam to E on the opposite side.
These two cams raise the brass block G and give the requisite support to
the cylinder F when the pressure is applied.
These are the chief characteristics of the lithographic press, and as
such they require not a little attention and intelligent manipulation.
It is practically impossible to secure a steady and uniform pressure
unless the scraper and tympan are carefully adjusted.
[Illustration: FIGS. 6 and 7.]
The former must be perfectly true with its V-shaped edge nicely rounded,
and the latter tightly stretched on the frame C so that it will not sag
or bulge when pressure is applied and the scraper passes over it. To
reduce the enormous friction caused by this pressure the back of the
tympan is usually dressed with a mixture of tallow and plumbago, a
dressing which requires frequent renewal. The plumbago possesses but
little body, and its salutary effect soon passes away. To prevent this
and to increase its adhesiveness it is sometimes mixed with a little
gum. A mineral black which is found in large quantities in the west of
England is even more effective than plumbago for this purpose. It forms
a strong and flexible dressing for the leather, is peculiarly adhesive
and provides an efficient lubricant.
It is a decided advantage to have two tympans in use, one for small
stones and another for the larger sizes. It is obviously unwise to pull
a number of impressions from small stones with a large tympan, for if
this practice is persisted in the tympan leather not only loses its
shape, but becomes perceptibly thinner on such parts as may have been
most subjected to pressure.
For similar reasons it is advisable to have a number of boxwood scrapers
of different sizes. The "dents" produced by a small stone on a large
scraper can only be removed by planing.
In lithographic press work some form of elastic bedding placed
underneath the stone will not only materially assist the pressure, but
will also minimise the risk of breakages. In fact, the pressure is
frequently so keen and of such a direct character as to render this
arrangement little short of a necessity. Extra thick linoleum will serve
this purpose admirably, and a zinc covering for this bedding will
complete the equipment of the lithographic press.
[Illustration: FIG. 8.]
The operations directly associated with lithographic press work are of
sufficient importance to warrant a full description of each, and will
form the nucleus of the following chapter.
CHAPTER VI
LITHOGRAPHIC PRESS WORK
Preparing the Design--Treatment of an Ink Drawing--Chalk
Drawings--Alterations--Value of Impressions--Offsets--The
Lithographic Hand-roller--Proving--Registration--General
Features--Transferring--A Commercial Necessity--
Arrangement--Choice of Paper--Transference to Stone--
Preparing the Forme.
The operations directly associated with lithographic press work are more
or less of a preparatory character. The preparation of a design, in its
progressive stages, from the lithographic draughtsman to the printing
machine, is usually carried out in conjunction with the press. Only
under exceptional conditions or for some particular class of work is the
lithographic press actually employed for printing purposes. Its ready
adaptability to the ever-varying thickness of lithographic stones, and
the manner in which pressure can be applied at will, as well as the
intense sharpness of such pressure, render it peculiarly suitable for
the work now under discussion. Such operations will be better understood
and probably more easily remembered if they are described in a sequence
such as might be presented under average commercial conditions. Taking a
design as it leaves the lithographic draughtsman, _i.e._ in the form of
a greasy drawing on stone, the first object of the printer is to so
prepare it as to preserve the conditions described in Chap. I. page 2.
This he may accomplish in the following manner.
Cover the whole stone with fresh strong gum and allow it to dry. Then if
it be an ink drawing, wash off the gum with water, and remove the
drawing ink from the surface of the design with a few drops of
turpentine and a piece of clean rag. Proceed to roll up with a
lithographic hand-roller charged with good black printing ink. The
consistency of this printing ink can only be determined by the character
of the work under treatment. It is therefore a matter of experience
rather than rule. Heavy designs covering large areas can be worked up
with moderately thin ink, while work of a finer description will most
probably require a stronger ink for its successful treatment. Between
these two extremes there is a variety of conditions and effects which
will require a ready recognition and an intelligent adaptation or
modification of any operation which may be described. It may even be
advisable to _rub up_ the work with a piece of soft rag and printing
ink, but the clearness and crispness of the drawing can best be
preserved by a complete removal of the greasy ink with which the drawing
was originally made. More particularly is this desirable when heavy,
solid work is in close contact with work of a finer description, for the
excessively greasy character of the artist's drawing ink has a dangerous
tendency to smear or spread and to thicken the design, unless a
reasonable amount of care is exercised. After rolling up the work as
well as possible, and having decided that it is firm and strong and is
fully charged with ink, dry the stone perfectly and dust over the design
with finely powdered resin or French chalk. With a piece of water of Ayr
stone polish away any scum or dirt which may surround the work, and etch
it quickly with a weak solution of nitric acid. Cover up with strong gum
and dry it. The design is now ready either for proving or transferring.
The treatment of chalk drawings, grained stones, or transfers from
grained paper needs a slight variation of the operations already
described. The preliminary etching is generally carried out by the
draughtsman by flooding the stone with a mixture of gum and acid, after
which the gum solution is allowed to dry. The chemical change which
takes place during this etching is often described as one in which the
soap present in lithographic chalks is changed to an insoluble compound.
This chemical change is perhaps a somewhat contentious matter, but the
effect and not the principle involved is to us the matter of primary
importance, and this effect is such as to actually prevent any spreading
of the design on the stone beyond the lines of the original drawing.
Returning once more to the operation, wash off the gum, and, having
removed the excess of water in the usual way, roll up firmly with a
strong black ink. Instead of washing out the drawing with turpentine
immediately, work off the original chalk by rolling up with a good nap
roller and taking frequent impressions. In this way the grain of the
drawing will be gradually developed and rendered fit for further
operations. The stone can then be passed to the prover or transferrer.
A French writer, in referring to the importance of really good _chalk_
drawing and printing, as well as to its artistic and technical value,
once said: "The printer requires a fair appreciation of that subtle
suggestiveness which gradations of tone can impart to a chalk drawing
before he can hope to successfully reproduce the artist's original
conception. A good printer handles his roller over a chalk drawing with
the same feeling as that with which a violin player handles his bow. By
movements rapid or slow, and by greater or less pressure over certain
parts, he charges the drawing to the proper tone."
If at any time the original work requires alterations, they may be
executed in the following manner. Roll up the design firmly in strong,
black ink, and, after fanning the surface dry, dust it over with French
chalk. Make the necessary erasures with water of Ayr stone and etch with
fairly strong nitric acid. Polish slightly, and wash well with a
plentiful supply of clean water. Pour over the stone a very weak
solution of alum, and again wash thoroughly with hot water, so that its
rapid evaporation may leave the work ready for immediate manipulation.
Alterations may be made by transferring or drawing. In either case it is
advisable to gum up the work with strong gum and allow it to stand until
dry. The subsequent treatment of any alteration will, of course, depend
upon their character and extent. As new work, they should be carefully
handled.
It is most important that a very _weak_ solution of alum should be used.
Being an alkali, a strong solution would have a tendency to dissolve the
greasy particles of the drawing and cause them to spread and thicken.
It is always advisable to take an impression from each design, whether
it be in ink or crayon, before it is laid aside for subsequent
manipulation. These impressions will not only reveal any inaccuracies or
weaknesses which might otherwise pass unnoticed, but also serve as a
useful record and for comparison with other transfers or impressions
which may be required.
There are other phases of preparatory work which come within the scope
of the lithographic pressman, and as they frequently constitute an
intermediary stage between the first drawing of the draughtsman on stone
and the making of transfer impressions to facilitate reproduction, a
description at this point will be appropriate.
It may be that a key forme only has been prepared, or perhaps an outline
forme with sufficient detail. In either case a number of offsets
equivalent to the number of colours necessary for the completion of the
design will be required. These are made by taking good, solid
impressions in stiff black ink from the key or outline forme. Dust these
over with a mixture of three parts Venetian red and one part lamp-black.
Lay them in convenient positions on a well-polished dry stone, and run
them through the lithographic press with a light yet firm pressure. The
result will be faint yet sufficiently clear offsets of an outline which
will enable the lithographic draughtsman to prepare any number of
formes, and these will register or fit each other and the original
drawing with perfect accuracy. Such outlines will in no way affect the
work of the draughtsman, and will disappear at the first application of
the gum sponge or moisture in any form.
[Illustration: FIG. 9.]
A lithographic _nap_-roller (Fig. 9) facilitates the work of the
pressman in the preparation and development of original drawings on
stone, and becomes an absolute necessity when crayon drawings on grained
stones are operated upon. The preparation and preservation of a roller
of this description requires a more than average amount of care and
attention. The best rollers are covered with French calf-skin with a
soft, velvet-like nap, and may be prepared as follows. Run the roller in
crude castor oil for a short time until the leather becomes soft and
pliable, then work out the superfluous oil by repeated rolling in medium
varnish, occasionally scraping off the varnish with a broad blunt knife.
Continue this for a day or two, then gradually work into the skin some
good non-drying black printing ink. The roller thus prepared may be
somewhat harsh, but a few days' use will bring it into condition. An
occasional application of tallow or lard, say about once a week, will
keep the roller skin soft and pliable, and counteract the hardening
effect of constant contact with the damp surface of the lithographic
stone and the oxidisation of the printing ink.
Proving the work of the lithographic artist, though not always an
absolute necessity, is a helpful and most important function. In its
progressive stage it enables both designer and lithographer to observe
the realisation of their colour schemes, and to amplify or minimise if
necessary the effects they desire to produce. Errors of judgment or of
detail can be rectified before the work reaches a more advanced stage.
Again, a finished proof offers something of a tangible character for an
expression of approval or disapproval, and serves as a useful and
helpful guide to the printer throughout the subsequent operations.
This will show clearly the importance of the prover's work, and though
it is not by any means an unusual proceeding to _prove up_ even the most
elaborate designs in the lithographic printing machines, it is, for
obvious reasons, more convenient to confine such work to the press. It
may therefore be regarded as an intermediate operation, distinctly apart
from the preparation of the original drawing which precedes it, and the
arrangement for machine printing which follows. The distinctive and
pre-eminently the most important feature of proving is the manner in
which one colour is registered with another; and although the methods
usually adopted are of the simplest possible character, the most
scrupulous care is requisite for their successful application. It
appears to be an almost ridiculous plan, so simple is it, to cut away
the angles formed by the register lines after the first printing (Fig.
10A), and then to place them to corresponding lines on each colour
forme, or to pierce the register lines as in Fig. 10B, passing a fine
needle through each puncture into corresponding holes drilled in the
stones and allowing the sheets to fall into position,--yet these
operations demand constant care and attention.
[Illustration: FIG. 10A.]
[Illustration: FIG. 10B.]
The mixing of colours for proving, and the general principle of their
application, are matters which are almost entirely under the control of
the printer. Their selection and the manner in which they are employed
are both determined by the individual character of the work. It is
impossible to indicate any "rule of thumb" guide for their application
or manipulation. The individual fancy of the artist, or the wish of a
customer, are the only probable complications which may have to be
considered. Then again, many phases of the work are more or less
experimental, when the resourcefulness of the printer may be tested, and
the mechanical features of his work be relieved by the exercise of
intelligent application, if not of artistic perception. Very rarely is
it possible to print from the litho-draughtsman's original drawing, and
even when it may be convenient to do so, it is, in the majority of
cases, unadvisable on account of the element of risk involved. There is
an ever-present danger of the stone breaking,--a catastrophe which would
necessitate an entire reproduction of the design, and even under the
most favourable conditions the constant attrition produced by the
rollers, etc., would have an appreciable effect on the work, and in
course of time destroy its value for graphic reproduction.
Many other equally cogent reasons why duplicates of the original should
be made for printing purposes present themselves. The chief of these is
an essentially commercial one. To reproduce half a million impressions
from a single small drawing would obviously depreciate the commercial
value of lithographic printing very considerably, and although there is
no record of the circumstances under which the duplicating of original
work by means of transfers was first evolved, it is only reasonable to
suppose that it was the direct outcome of a necessity which was as
peremptory in its demands as it has been far-reaching in its effects.
The method is one by which any number of impressions can be made on a
suitably prepared paper, and with a sufficiently greasy pigment. These
can be re-transferred to a lithographic stone, and in this way
facsimiles of the original may be secured and arranged in the manner
most convenient for machine printing. Great care is necessary in making
these transfer impressions. They must be perfectly solid, yet not
overcharged with ink, _i.e._ they must be clean and sharp, and as nearly
an exact replica of the original work as it is possible to make them.
That the further description of these operations may be as lucid and
practical as possible, we will apply it to ordinary work-a-day
conditions, and suppose that a design in three workings has been
lithographed and prepared for transferring as already described. The
size of the work is 7-1/4 in. by 4-1/2 in., then the paper on which it
is to be printed ought to be double crown, 20 in. by 30 in. This will
allow 1-1/2 in. for the gripper and 1/2 in. margin at the back and
sides. Sixteen transfers can be pulled from each colour forme on a thin,
transparent transfer paper. Mark out a sheet of stout paper as in Fig.
11, and arrange the transfers in the position indicated by the dotted
lines. The gripper margins A A are determined by the construction of the
machines, and may be varied accordingly.
Varnished transfer papers may be laid down on a slightly warmed dry
stone, and if French transfer paper be used the stone must be slightly
damped. If the sheet of transfers is laid down to a board--Fig.
12--uniformity of gripper margin will be assured throughout the series,
and the work of the machine printer facilitated.
[Illustration: FIG. 11.]
Pull it through the lithographic press with a gradually increasing
pressure in the usual way. The varnish transfer paper will be
sufficiently tacky to adhere slightly to the surface of the stone, so
that the pressure may be repeated again and again with perfect safety.
It may not be possible to remove the base upon which they were arranged,
as it is usual to secure them in position with paste. At this point the
manipulation of the two varieties of paper differs slightly. The thin,
transparent variety is usually fastened down to its paper base with
syrup, glucose, or some sticky composition of a similar character. This
paper backing can be removed immediately after sufficient pressure has
been applied to fix the transfers to the stone. As this transfer paper
is adhesive it is necessary to damp the surface of the litho-stone
before it is laid down, when, of course, it will readily adhere, even
under a moderately light pressure.
[Illustration: FIG. 12.]
The further preparation of work, after being transferred in this manner,
is in many respects similar to the treatment of new work, but with this
important difference. A new transfer should almost invariably be worked
up with a soft rag and black ink, the latter being thinned down with
turpentine and varnish. Gum up the work, and allow the gum to dry. Roll
a piece of soft rag into a pad, and charge it with printing ink which
has been thinned down. Wipe off the gum on the surface of the stone,
leaving only a thin film over the work. Rub up the transfers with the
rag already prepared, and when fully charged with ink cover them with
fresh gum. If possible they should stand for one or two hours, when the
rolling up and etching may be proceeded with.
Accuracy of register can be ensured by the second and third sets of
transfers being patched up to the first forme in the following manner.
Make two fairly strong black impressions of this forme on a stout
unstretchable paper. Fix these up on a glass frame in such a position as
to allow the light to pass through them, and carefully place each
transfer in its exact position. They can then be laid down on separate
stones in the same way as the first set. These are the simple outlines
of the transferring process. In detail they may, of course, be modified
to meet the exigencies of peculiar conditions, which in lithography are
frequently the controlling powers, and at all times are matters of vital
importance.
CHAPTER VII
MACHINE PRINTING
The Printing Machine--The Halligan--Some Mechanical
Phases--Speed--Pressure--Levelling the Stones--Cylinder
Brake--Inking Rollers--Damping.
Concerning the structural qualities of the various types of lithographic
printing machines now in use, much might be written and divers opinions
expressed. In this respect, however, it would be invidious to suggest
that one maker's machines were better than another's, and such would be
the natural trend of a discussion on these lines. The machines all have,
it is true, many points in common where comparisons would be legitimate
and easy. Yet, on the other hand, they each possess distinct advantages
which will no doubt appeal to the printer individually, in proportion to
their suitability or otherwise for his particular work. Conviction will
follow experience in these matters, and any decision arrived at after
this fashion may be regarded as a useful and valuable acquisition.
The illustration on page 35 (Fig. 13) gives a fair general idea of the
modern lithographic machine.
Fig. 14 illustrates a somewhat novel type of lithographic printing
machine, in which the gripper is entirely dispensed with, the sheet
being held to gauges by the operator until caught between the small
cylinder and the stone, when pressure is immediately applied. The stone
is simply blocked up in the bed of the machine and the position of the
print on the paper assured by moving the gauges. This useful little
jobbing machine is a decided innovation, and the simplicity of its
construction is only equalled by the precision of its movements.
[Illustration: FIG. 13.]
Lithographic machine printing presents many peculiar features, each one
of which requires careful and constant attention for their successful
operation. Some of its purely mechanical aspects--the care of the
machine and its accessories, together with their various functions and
applications--offer a wide scope for resourcefulness and ability of a
high order. The primary purpose of the machine itself was undoubtedly to
accelerate the reproductive power of lithography from a commercial point
of view; and throughout the entire course of its development the aim of
the engineer has been to produce a printing machine with an
ever-increasing capacity for reproduction. It does not follow, however,
that the printer's responsibility has been proportionately increased.
Mechanical appliances have now so far superseded hand labour that, apart
from a thorough knowledge of the principles of lithography, which is in
itself essential, successful lithographic machine printing is largely
due to resourcefulness, alert perception, and a skilful blending of
mechanical and technical knowledge.
[Illustration: FIG. 14.]
Passing over the vast amount of detail which is usually and almost
invariably associated with machine printing, but which offers little
that is new to the practical worker, it might be advantageous to discuss
a few points which are too often overlooked.
Speed, as has already been pointed out, is a very important factor in
lithographic machine printing. It has become quite a necessity, and
everything which conduces to it should receive the most careful
consideration. Economy of power is too seldom regarded as a standard of
efficiency in the printer. At any rate, as far as this is concerned it
is doubtful if he fully realises the effect of what may appear to him
as insignificant matters. A little pressure more or less on the stone
may be in itself a mere trifle, so also would be a careless arrangement
of the inking rollers or indiscriminate damping of the stones, yet, when
taken together, what a considerable waste of power they might cause;--a
waste which is altogether unnecessary and could easily be obviated by
care and forethought. Excessive pressure is frequently resorted to in
order to "bring up" an impression which is defective owing to some error
of judgment in its preparation. It undoubtedly secures the desired
effect, but at what a cost! There is a proportionately heavier drag on
the machine and a greater strain on its most vital parts. The following
view of this matter may be regarded as somewhat exaggerated, but it is
by no means an uncommon state of affairs, and will at least serve to
emphasise the importance of this point. It is a popular fallacy to
suppose that in adjusting the litho-stone to the bed of the printing
machine it should be made _perfectly level_. As a matter of fact a much
easier and more satisfactory impression can be made from a stone which
is worked just a little higher at the front or gripper edge than at the
back, and for this reason. The drag on the cylinder as it makes the
impression is appreciably greater at the back than at the front, and
when the pressure is heavy it has a tendency to leave the back edge with
a very decided jerk. The remedy is obvious and simple. As already
suggested, the stone should be set in the machine with the least
possible inclination towards the front. This adjustment is easily
effected by a judicious arrangement of a few layers of brown paper. Just
think for a moment of the effect likely to be produced by such a jerk or
jar, which would under ordinary working conditions occur from twelve to
fourteen times per minute whilst the machine was in motion! Abnormal
pressure would of course intensify the strain, and sooner or later
produce results of a decidedly disastrous character. Under the most
favourable conditions this continual springing would tend to move the
stone out of position, and thus affect the register of one forme with
another.
Another certain result of this condition of things is, that the sharp
pressure on the back edge of the stone would almost certainly cause an
appreciable indentation in the cylinder covering. This would eventually
cut through, or at least interfere with the working of a larger sheet at
some future time.
The mechanism for raising or lowering the lithographic stone in the
machine for the adjustment of pressure is comparatively simple (Fig.
15).
[Illustration: FIG. 15.]
There are two screws similar to A which pass right through the feet of
the stone carriage B B. A movement of the screws will therefore cause a
corresponding movement of the stone carriage on the blocks or inclines C
C. The lock-nut D holds the screw securely once the pressure is
adjusted.
So few printers really understand the proper adjustment of a cylinder
brake that some information concerning it will no doubt prove
acceptable. In the first place, a continuous action brake which can be
released at certain intervals is most suitable. It holds the cylinders
perfectly rigid whilst the machine is running free, and applies a
sufficient check at the points required. The intermittent movement
referred to is obviated in various ways. Fig. 13 shows an example of one
which is both simple and effective. It might be well also to explain the
principle and purpose of the cylinder brake. It is almost impossible to
cut mechanical gearing which will run easily and yet be entirely free
from _slogger_. Consequently the revolution of a printing machine
cylinder would be more or less jerky unless steadied in some way. This
is especially the case when it reaches the stone, and, owing to the
pressure applied, lifts a little in the gearing. A recognition of this
simple matter will enable an intelligent workman to arrange the brake
action with judgment and effect.
[Illustration: FIG. 16A.]
A comparison of the old arrangement of inking rollers (Fig. 16A) with
the new (Fig. 16B) is in itself an object lesson in this question of
power and its economical application. It is but reasonable to suppose
that the power required to move a set of rollers arranged in the
old-fashioned manner (Fig. 16A) will be infinitely greater than that
which would be needed for such an arrangement as shown in Fig. 16B.
[Illustration: FIG. 16B.]
Pursuing this matter still further, the question of indiscriminate
damping presents itself. Granted that the influence here is an indirect
one, yet it is a cause which frequently leads to an undesirable finish.
Every printer knows something of the effect produced by excess of water
upon printing inks. It hardens and stiffens them by accelerating
oxidisation. In course of time their free working on the rollers is
interfered with, and loss of power is by no means the worst result. Weak
and impoverished impressions, abnormal wear and tear of the printing
forme, and excessive saturation of the paper may follow.
In lithography generally, and in lithographic machine printing
particularly, the damping of the stone is a matter which requires
constant and careful attention; any arrangements for this purpose should
therefore be as effective as possible. The damping rollers should be
thoroughly cleaned each day, in order to remove any scum or grease which
may have been collected from the printing forme.
[Illustration: FIG. 17.]
The arrangement of damping rollers shown in Fig. 17 is a decidedly
practical one. The upper roller consists of metal, usually brass or
zinc. It collects any accumulation of ink or scum from the actual
dampers, and can be cleaned at any time without serious interference
with the progress of the work. Its adoption, however, has not been very
general, although it would be difficult to ascribe any good reasons for
such a fact.
CHAPTER VIII
MACHINE PRINTING--_continued_
Register--Atmospheric Conditions--The Key--The Gripper--
Starting the Machine--Fixing the Stone--Strength of
Colour--Grit--Making Ready--Regulation of Speed.
It is almost impossible to overestimate the importance of register in
lithographic machine printing, and any suggestions which are likely to
be of assistance to the printer in this matter will no doubt be
welcomed.
Variable atmospheric conditions, insufficiently matured paper, or
constitutional defects in the machine, are frequent sources of
inaccurate register. These may be to some extent unavoidable and
therefore beyond the printer's control, but there are numerous other
points which have an important bearing upon the accurate fitting of one
colour or forme with another, and therefore require care and attention.
The following method of procedure is well worth consideration, as it has
decided advantages over many others.
The _key_, or outline forme, to which the colour formes have been set
up, is put into the machine at the beginning of the printing operations.
The exact position of the design on the sheet is arranged, and twenty or
thirty impressions taken on a reliable paper. With these impressions as
a guide it is a comparatively easy matter to register each colour
accurately. This effects a saving both in time and material, and rarely
fails to produce satisfactory results. During the early stages of the
printing, when it is difficult to detect any slight movement of the
stone in the machine, a sheet bearing an impression of the key may be
printed in the usual way, when any variation in register will be
revealed at a glance. The relative positions of the side lay and gripper
seldom receive the consideration they ought to have. The gripper and
side lay should be exactly at right angles to each other, and any
divergence whatever from this rule simply courts disaster. If they form
an acute angle there is a danger of the sheet moving _forward_ a little
as the gripper closes. If, on the other hand, they are fixed at an
obtuse angle, there is a proportionate risk of the sheet falling back as
the gripper closes. If any degree of uniformity could be guaranteed in
these movements, then all would still be well, but unfortunately no such
guarantee can be given, owing to a possible variation in the cutting of
different batches of paper.
[Illustration: FIG. 18.]
Another matter of a similar character and quite as important in its
issues is more directly connected with the gripper.
The type of gripper shown in Fig. 18 is probably the best for general
use. It enables the printer to use two or more pins upon which to rest
his sheet, according to the particular requirements of his work. Two
pins are usually sufficient and answer best, for the following reasons.
It is by no means unusual to find that the paper, trimmed though it may
be, has slightly convex or concave edges, owing either to insufficient
damping or an inaccurate setting of the knife in the guillotine cutting
machine. This can, of course, be avoided, but the point at present under
consideration is one of _possible_ effects. This contingency and its
effect are considerably exaggerated in Figs. 19A and 19B, but for
purposes of illustration the suggestiveness of the two sketches is not
at all too emphatic.
[Illustration: FIG. 19.]
Start the machine with a light pressure, for once the stone is locked up
a certain amount of danger will always exist if at any time it is
necessary to reduce the pressure. The stone may still be held by the
blocks, even after the bed of the machine has been lowered, only to come
down with a snap when pressure is applied. Such a danger might, of
course, be averted by slackening the screws and blocks; but then the
stone would almost certainly move out of position and the registration
of the forme be altered.
Narrow slips of paper folded two or three times, and inserted between
the block and the stone, will often check any tendency the latter may
have to lift when the screws are tightened.
Of the many annoyances associated with the lithographic machine
printer's work, _grit_ is probably the most troublesome, inasmuch as its
presence is almost imperceptible, while its effect is extensive and
often disastrous. Its sharp grains become embedded in the inking-roller
skins, and plough tiny furrows across the printing forme, doing much
damage before the printer realises the presence of any foreign matter on
the inking-rollers. Prevention is a simple matter enough, but a cure is
rarely, if ever, accomplished. Dust the rollers and examine them
carefully before commencing operations, and in this way ensure perfect
cleanliness. It may seem a trifle, but it is none the less an important
one, and perhaps the reader has already realised that "trifles make
perfection, and perfection is no trifle."
[Illustration: FIG. 20A.--Patent conical counter shafting.]
[Illustration: FIG. 20B.--Patent conical counter shafting.]
[Illustration: FIG. 21.]
In _making ready_ on a lithographic printing machine, as in almost every
phase of industrial life, method is the great secret of success. Method
conquers the most stubborn difficulties, and, though it is not at all
times profoundly interesting in its application, yet it more than repays
any monotony it may involve. In the matter of lithographic printing, at
any rate, a few methods of an essentially simple character might be
cultivated with advantage. This chapter is not intended as a complete
record of such methods, but a number of items are discussed herein
which, though simple, are intensely practical, and likely to suggest
more to the reader than is found described in the text.
The question of speed may sometimes seriously handicap progress. It is a
self-evident fact that the solid impression of a heavy poster cannot be
made at the same speed as a light tint in chromo work. Speed cones are
usually fixed to a counter-shaft to regulate the speed of the machine as
required. Figs. 20A and 20B show an improved arrangement of this
character, in which tapering drums A A are substituted for cones, the
belt being moved and held in any position by the screw and forks B and
C. D is the driving pulley which transmits the power to the machine.
Electricity as a motive power for printing machinery is quietly yet
irresistibly winning its way into general favour, and for very cogent
reasons. It is the most convenient form of motive power, and can be
transmitted for long distances without any appreciable loss. It takes up
little space, and almost entirely dispenses with belts and shafting. It
is also essentially economical, because it can be applied to the
smallest press just as easily as to a 60' by 40' poster machine (Fig.
21).
CHAPTER IX
LITHOGRAPHIC COLOUR PRINTING
A Commercial Value--Peculiar Features--Colour Sequence--
Controlling Elements--A Question of Register--Suitable
Paper.
As a commercial phase of lithographic printing, colour printing offers a
vast and ever-widening field of usefulness. Nor is it altogether
deficient in these artistic qualities which are pre-eminently
suggestive, as well as attractive and artistic. Colour printing, in its
application to lithography, is in many respects peculiar. It is not what
might be described as a self-contained process; for its successful
realisation depends as much upon the harmonious and skilful combination
of colours in the design as upon the manipulation of the printing inks,
the sequence of the colour formes, and their accurate fit or register
during the actual printing. The most excellent printing would produce
barely passable results unless the design was effectively arranged, and
prepared with some consideration for the conditions under which it might
be printed. Nor is it at all unlikely that a design, however smart and
artistic it might appear in its original form, would be irretrievably
spoiled by clumsy handling or careless printing. The subject for
immediate consideration is the practical employment of printing inks for
the reproduction of coloured designs, their qualities, peculiarities,
and relative values, as well as the means employed to make them amenable
to commercial conditions. An intelligent appreciation of these points
will not only extend the possibilities of printing inks, but will also
enable the machineman to accentuate their attractive and suggestive
power.
"Colour is to design what salt is to food," and successful colour
printing has been very aptly described as the adaptation of printing ink
to the ever-varying character of work and conditions of employment. This
very practical definition will form the keynote of a chapter which, by
the very nature of things, must be to some extent authoritative and
comprehensive. The colour sequence, _i.e._ the order in which the
colours must be employed to secure the best and most economical results,
is of primary importance in colour printing. On broad lines, the
principle usually followed is one in which the opaque colours are
printed first, and upon these all secondary effects are built up. This
building up of colours plays also a most important part. Its relation to
colour sequence is a necessary and influential one. For example, it
might not be absolutely essential that even a yellow should be printed
first, if it did not form the base for the building up of a green by the
super-position of blues, of an orange effect in conjunction with red, or
as a secondary flesh tone under the buff.
The difference between printing a blue over a red or _vice versâ_ is
also very striking. One produces a purplish-black brown, and the other a
rich chocolate-brown. Other complications of a similar character are
common, but these will indicate with sufficient clearness the possible
modifications of colour sequence.
Another feature upon which colour sequence in printing largely depends
is the point at which the outline forme can be most effectively
introduced. It is advisable to print the outline forme at as early a
stage as possible for obvious reasons. Perfect registration is far from
easy to secure. Red in the lips, blues in the eyes, and isolated touches
of colour in various parts of the design must fit the browns, and
therefore fit each other, and yet they may have no direct relation to
each other in the printing. A remedy has been already suggested, but
once an outline forme is printed the cause of bad registration is to
some extent removed, and a remedy quite unnecessary. When worked on
reasonable lines it is frequently an advantage to make the outline one
of the earlier printings, so that any harshness of contour, etc., may be
toned down by the succeeding greys. It is often a matter of personal
opinion, or perhaps of circumstance, which decides the final printings.
The pink may be reserved to impart brilliancy and warmth to the prints,
or it may be equally suitable to hold back a grey, and, by regulating
its tone and strength, soften down any tendency to hardness, pick out
the darker prints, and emphasise the shadows. Even these suggestions,
although usually regarded as standard ideas, must be subjected to
modifications under certain conditions.
Here is a practical instance. Unless paper is unusually well seasoned
and of first-rate quality, the temperature of the workroom equable, and
the printing machine in good order--a combination of excellences which
is unfortunately rarely met with--the colour sequence must be of a
fairly elastic nature. To print a gold first is quite usual, because the
bronze powder will persistently adhere to any preceding printings. From
that standpoint alone such a procedure would be eminently practical and
convenient, but suppose for a moment that the gold must fit a later
printing with absolute accuracy, _e.g._ an outline forme, or as forming
the base for some ornamental scheme, then the difficulties which arise
are somewhat trying, and for this reason. The paper being new, the most
serious distortion of any kind is likely to occur during the first
printings, and so long as yellows, fleshes, or other colours of a
similar character are printed first, no serious difficulty is likely to
arise; but with the gold printing it may be altogether different. It is
quite possible to make both yellow and flesh dry dead, _i.e._ without
even sufficient tack to catch the almost impalpable bronze powder. At
the same time, care must be exercised that the colouring matter is not
left dry on the surface of the paper owing to its separation from the
reducing medium. This plan has been adopted under actual commercial
conditions and with conspicuous success, and it is therefore offered as
a preventive measure which is free from many drawbacks which are the
frequent accompaniment of novel ideas and operations. Here then is a
simple practical summary of the idea. The yellow and flesh, or
equivalent colours, are printed first, so that they will dry free from
gloss or _tack_. The fit required between such colours and subsequent
printings is generally a matter of minor importance, and at this stage
distortion of the paper, whether it be by stretching or contracting,
will not seriously depreciate the value of the print when completed.
Register between the gold and an outline is frequently of an entirely
different character, and in many cases the slightest variation will be
readily discernible, and have a decidedly bad effect on the finished
work. Apart from this, the questions which decide or control the colour
sequence have been clearly indicated previously.
This matter may be one of convenience also, for unless otherwise
predetermined it would be unwise and far from economical to print a blue
before a yellow, or a black before a red, etc. The amount of cleaning up
thereby involved would become a serious and distinctly disagreeable
item, and purity of tone in the lighter colours would be conspicuous by
its absence.
The matter of well seasoned printing paper has been already referred to.
For effective colour printing the paper must also possess several other
essential qualities. It should be firm in substance, sufficiently
absorbent to carry the successive layers of printing ink, as far as
possible unstretchable, and should present a smooth surface though not a
glazed one. The chalky, dull, enamelled papers offer many recognised
features of value to the colour printer. They assist in the absorption
of the ink as well as afford a suitable surface for their impression.
Friction-glazed and other prepared papers are also excellent for colour
printing by lithographic methods.
CHAPTER X
LITHOGRAPHIC COLOUR PRINTING--_continued_
Printing Inks--Varnish--Reducing Medium--Relative Values--
Some useful Hints--Bronze Blue--Vermilion--Ink Mixing--
Ceramic Transfers--Colour Transparencies.
For the successful manipulation of printing inks of any description it
will be necessary to know something of their composition, or at any rate
of such features as render them peculiarly suitable for printing
purposes. From a printer's point of view the most important of these
features is what may be described as the reducing medium, _i.e._ the
medium which holds together the various colours so as to produce
pigments of suitable working consistency. The most useful and the
commonest form of reducing medium is a linseed oil product, known in its
prepared state as a lithographic varnish, with a supplementary title
indicating its specific character. Its value to the lithographic printer
lies mainly in the fact that when it is fully matured it possesses a
good full body along with fair drying properties and freedom from any
excess of greasy matter. This varnish is used in three or four
consistencies between which any degree of strength may be arranged by
mixing. A brief outline of the manner in which they are prepared may
still further emphasise their usefulness in lithographic printing.
Raw linseed oil is matured and oxidised until its consistency is
considerably reduced. It is still further reduced by being boiled at a
high temperature, and is known commercially as "boiled linseed oil." As
this boiling is continued the fumes which quickly rise can be ignited,
and the liquid soon assumes a syrupy or stringy character, according to
the length of time during which it is subjected to the action of fire.
By extending or discontinuing the burning the varnish is produced in
three grades--thin, medium, or strong.
Lithographic varnish is a good servant but a bad master, and it is a
generally recognised fact that, beyond a certain point, lithographic
varnishes as a reducing medium will depreciate the value of colour.
The chief requisite in colour printing is the production of a solid flat
impression, and for this purpose almost all printing inks must be
reduced to a suitable working consistency. To accomplish this, and at
the same time retain the full colour strength of printing ink, a soft,
free-working composition will be useful and desirable.
There are several commercial varieties of solid oil from which the
excess of grease has been extracted. These form excellent reducing
mediums. They break down the _tack_ of stiff pigments and enable them to
work freely during the printing operations. The drying of inks thus
prepared is not seriously retarded; they _lift_ readily and usually
produce brilliant impressions. There is a reasonable and logical
explanation of these peculiarities which is both interesting and
suggestive. Whatever the character of a reducing medium may be, its
effect on the strength of colour will of course be in proportion to the
quantity used. In all probability 1 oz. of a solid oil composition,
otherwise known as lithographic reducing medium, would soften down a
quantity of printing ink for which at least three times its bulk of
varnish would be required. Consequently, the depth of colour and
covering power of an ink reduced with "litho medium" would be
proportionately greater than that reduced with varnish. Vaseline in
some of its commercial forms is frequently used by American printers,
and even in this country its use is being tardily, though none the less
surely, recognised.
A few remarks anent the _intelligent_ application of a softening medium
may not be inopportune. Considerable care and judgment must always be
exercised or there will be a loss of cohesion in the colour pigments
which cannot fail to prove disastrous. The tendency of lithographic
varnish is to bind the colour pigments together, and this should not be
entirely counteracted by the addition of fatty compositions, lest the
printing inks run "scummy" during printing operations, and in drying
leave the colouring matter, from which they have been detached, on the
surface of the paper in the form of a dry powder.
Such lack of cohesion may, however, be an inherent feature of the ink
itself, and not be produced in the manner just indicated. Bronze blue
affords a striking example of a printing ink of this character. It is,
in fact, a "constitutional weakness" which cannot apparently be
prevented, but which is fortunately not incurable. The addition of a
little Canada balsam to bronze-blue ink will add considerably to its
working qualities. The loose particles of the pigment appear to be held
together without becoming harsh or stringy, as might easily happen if
varnish of sufficient strength was added to produce the same effect.
Other colours, again, such as vermilion and yellow, owing to their
weight and texture, will always require a fair percentage of varnish in
their composition. At the same time, a little reducing medium might also
prove beneficial. Referring once more to the fact that vermilion, as
distinguished from its imitation, is unusually heavy, etc., it may be
useful to know that for "blocking out" work it has no equal in all the
range of printing inks. It possesses unrivalled opacity, and as a
"blocking-out" agent frequently plays an important part in colour
printing.
Of the other printing inks, few possess characteristics of a
sufficiently striking character to require special mention. Their
working qualities present no exceptional difficulties, and their
employment either under primary or secondary conditions is almost
invariably determined either by the character of the work or some such
conditions as have been already indicated.
When the strength of a colour is problematical, or its effect more or
less a question of experiment, it is a safe plan to mix it a little
lighter than will be required. For obvious reasons it is much easier to
alter the line or tone of a light colour than that of a darker one.
The arrangements for extensive and economical ink mixing need not be of
a very elaborate character. Standard colours might with advantage be
mixed in large quantities and kept as stock shades. Fleshes, pink,
blues, greys, etc., are all useful colours which are in constant use. A
warm or cold tone could be imparted to a _stock_ grey as required, and a
similar method adopted with regard to the other colours. Other peculiar
conditions could be met in a similar manner, and many economies thereby
effected.
Although the foregoing remarks refer mainly to lithographic colour
printing generally, they may with equal effect be applied to many of its
more specific branches.
Colour printing for tin-plate decoration will be fully discussed in a
subsequent chapter.
Transfer printing for ceramic decoration presents many features in
common with transfer printing for metal decoration. Printing colour
transparencies is a commercial phase of colour work which is productive
of many curious and attractive effects. Unlike the ordinary colour
prints, the transparency is intended for exhibition both by reflected
and transmitted light. The paper is of a thin, tough quality, and the
first printing is usually a white of good covering power and exceptional
opacity. It is not necessary to print a solid white groundwork for the
coloured design. If an intense brilliant colour is required by
transmitted light the omission of part of the white printing will add
considerably to the effective character of the design. A brilliancy
secured in such a manner may be still further intensified by printing
the colour or colours in register _on both sides of the paper_. This can
be easily accomplished by first allowing the cylinder covering to take
an impression from the stone, and then, with the sheet laid in the
gripper, make a second impression in the usual way immediately after.
The first print, which might be termed the transfer, will then be made
in accurate register on the back of the sheet.
Semi-transparent, or even transparent, effects can be obtained with any
of the colours by an omission of the white printing from the parts
affected. Complete opacity may be secured by its introduction.
This print is afterwards rendered more or less transparent by coating it
with a suitable varnish.
CHAPTER XI
SUBSTITUTES FOR LITHOGRAPHIC STONES
Metal Plates--Preparation--Manipulation--Descriptive
Details--Machine Printing--The Printing Bed--Rotary
Printing Machine.
Metal plate, as a substitute for stone, is now such an important factor
in lithography that the printer who wishes to consider himself
thoroughly efficient must possess a fairly comprehensive and practical
knowledge of its manipulation and possibilities.
The prejudice which has hitherto checked the progress of this branch of
lithography was not altogether of an unreasonable character. The plates
themselves were far from reliable, and the difficulties resulting
therefrom were a fruitful source of trouble and expense.
Metal, as a printing surface, is even yet a comparatively new factor in
lithography, and the majority of printers have been working with
lithographic stones from their apprenticeship till the present time. It
is not surprising, therefore, that in relation to the use of stones
almost every possible contingency has been provided for, but with metal
plates a little fresh knowledge must necessarily be acquired before the
workman can claim the same familiarity of manipulation which he may feel
towards the parent process. This is, in fact, the point upon which the
whole question usually turns. Good work can be produced from zinc and
aluminium plates,--of that there is not the slightest doubt,--and it is
equally certain that the advantages offered by their use are of a
substantially practical character. They can be handled with ease and
with absolutely no fear of breaking. They are much less costly than
stone, and require less storage room.
A grain of a finer and sharper texture can be imparted to metal than is
the case with stone, and what is even of greater importance, the
character of such a grain remains unaffected for a considerable time.
Surface inequalities are rarely met with in metal printing surfaces, and
consequently uniform pressure is to a certain extent guaranteed. In
photo-lithography it is possible to make a print from a negative direct
on to the plate (Chap. XVII. page 100). This ensures an original of
exceptional clearness and strength, especially in half-tone subjects.
Although an ordinary zinc plate, which has been carefully polished to
free it from every trace of grease, can be used for lithographic
printing, the best results are obtained from plates which have been
specially prepared. A slight de-polishing with pumice sand and a piece
of felt may impart the requisite "tooth" to the face of the plate, or
the following method may be adopted:--Clean the plate with pumice sand
and felt, and immediately immerse it in a hot bath containing:--
18 oz. Water.
1/4 oz. Alum.
1 dram Nitric acid.
Keep this liquid in constant motion over the face of the plate until it
assumes an even, silvery-grey appearance, and then wash it thoroughly
with a plentiful supply of clean water. Dry at once, and quickly.
These plates can also be sand-grained by specially constructed
machinery, or a variety of grains and stipple can be imparted to their
surface by etching or sand blast.
A novel yet practical idea, which has met with considerable success, is
to electrolytically prepare the surface of the plates. The value of this
preparation has been amply demonstrated by its extensive adoption and
successful use. Another distinctly progressive feature is a deposit of
alumina on the zinc, which for printing purposes gives it all the
advantages of an aluminium plate.
[Illustration: Plate-graining machine, showing oscillating motion.]
Transfers can be made on metal plates in much the same manner as on
lithographic stones. For press work mount the plate on a piece of
cardboard its own size, then, having gummed a sheet of brown paper on
the face of the litho-stone, place the mounted plate near the centre and
fasten it with paste or gum. This will prevent it moving about, and also
raise it sufficiently from the stone to enable the printer to use his
damping-cloth and roller freely. Before mounting, the back of the plate
should be carefully dusted to free it from grit and dirt.
After the drawing or transfer has been made cover the surface of the
plate with strong gum, and while this is still wet add to it a solution
of bichromate of potash. Leave a slight film only of the gum bichromate,
and then dry it quickly and thoroughly. Wash out the work with
turpentine, _not with water_. The gum, being insoluble in turpentine,
remains unaffected.
[Illustration: Plate-graining machine, showing interior of trough.]
Roll the plate up _solid_ in black ink, sponge it over with water, damp
it with a cloth, and then roll it up in the usual way. When the work
becomes fully charged with ink, dust it over with a mixture of resin and
French chalk, and etch it with the acid etching solution.
Every maker of zinc and aluminium plates supplies this special etching
solution, prepared for a certain quality and character of metal. It is
advisable, therefore, to use the preparation recommended, and thus avoid
the many pitfalls which beset the path of the experimentalist.
"The plate is now well washed over with clean water, and _thinly_ gummed
up. When the gum is dry wash out the work on the top of the gum with dry
flannel or felt till all the work is removed, sprinkle a few drops of
water on the plate, and with a rubbing-up rag and a little ink and turps
rub up the work till it is gently charged with ink, then roll up till
work or transfer looks strong and sharp, when the plate is ready for
printing."
For etching and rolling up chalk drawings on grained plates: "Pour in a
saucer some of the etching solution, and add about the same quantity of
fresh, strong gum. This solution is evenly distributed all over the
plate with a camel-hair brush, and left to dry. Then the etching is
removed with water, and the plate very thinly gummed up and left to dry.
Now the work is washed out with turps and a piece of dry, soft felt or
flannel, _without water_, till all the work disappears, and the plate
rolled up solid black. Then sponge over with water-sponge, damp over and
roll up till work appears nice and sharp. Now dust over with resin and
French chalk, and etch again with the etching solution, full strength.
After the etching has dried remove the same with water, and gum up
again.
"When drawings are to be washed out for proofing or printing, the plate
should first be thinly gummed up. This gum layer is left _to dry
thoroughly_, and is not removed when the work is washed out (without
water) with turps and a dry piece of flannel or felt. Next wipe away all
the black ink and turps, still using no water for this operation. Should
any black work be left, use some more turps on the _clean dry rag_ till
all the work has been removed, then sprinkle a few drops of water on the
plate, and use a clean rag to remove the gum layer and loose black ink
left on the plate, then damp over as usual and roll up.
"Plates treated in this way retain the grease contained in the drawing,
and the work rolls up easier and quicker, and none of the finer work
gets weakened or lost; also, the plate keeps cleaner and free from scum.
"When alterations are necessary the work should be rolled up with a
strong black ink, and dusted over with French chalk (powdered talc).
Remove the part which requires altering with a mixture of equal parts
etching solution and turpentine on a small piece of felt or flannel, and
rinse well with water. Pour some special re-preparing solution in a
saucer, and apply this solution with a camel-hair brush to the parts
where the work has been removed; after the solution has remained for a
few seconds rinse well with water. This operation is to be repeated
several times till the surface looks clean, no work being visible; and
after the plate is dried with clean white blotting paper it is ready to
receive the additional work. When the alteration has been made, the
rolling up should be done with the bichromate solution, as per general
directions.
[Illustration: FIG. 22.]
[Illustration: FIG. 23.]
"Where the alterations involve additional work only without erasures
roll up the design first with a good, strong ink, and dust over with
French chalk. The special re-preparing solution is used in the same
manner as acetic or citric acid is employed on a litho-stone. For this
purpose we recommend that the special solution should be diluted with an
equal quantity of clean water, and the solution applied with a
camel-hair brush. It should remain on for a few seconds, and then be
quickly rinsed with clean water. This operation may with advantage be
repeated two or three times for securing a clean surface for the
additional work. When the plate has been thoroughly dried with clean
blotting paper it is ready to receive the additional work. The rolling
up should be done with the bichromate solution, as per general
directions."
Machine printing from zinc or aluminium plates requires but a slight
modification of well-known methods; and although it may in some respects
present entirely new features, the making ready of work in which several
printings are employed is simplified, and consequently much time is
saved. In the ordinary type of litho-printing machine the printing bed
(Fig. 22) is levelled in the machine for the first printing, and, if
this is carefully arranged, no alteration will be required throughout
the whole series; for, in changing from one colour to another, the
printing plate can be slipped from the bed and another substituted in a
very few minutes. The most scrupulous care should be exercised at all
times to prevent dirt or grit of any kind insinuating itself between the
surface of the printing bed and the back of the plate.
It is not in connection with the flat-bed printing machine, however,
that the most decided progress is likely to be made in surface printing
from metal plates. "The change which is already foreshadowed in the
printing mechanism of to-day is shown by the growing demand for the
rotary in place of the slow and tedious movements of the flat-bed
press."
The mechanical principle of the rotary machine (Fig. 23) at once
suggests an absolute precision of movement which it is scarcely possible
to guarantee in the flat-bed press. There is no appreciable lift in the
gearing of the cylinders when the impression is made, and practically no
risk whatever of _slogger_, such as that described in Chap. VII. page
38. The uniform velocity of the cylinders, which is to a great extent
due to the points already indicated, considerably reduces friction,
produces perfect registration, and enables the machine to be worked at a
high rate of speed. The machine shown on page 63 presents many novel and
essentially practical features. The side elevation (Fig. 24) gives a
fairly accurate idea of its general mechanical principles.
[Illustration: FIG. 24.]
CHAPTER XII
TIN-PLATE PRINTING
Its Evolution--Transfer and Direct Transfer Printing--The
Coated Paper--Reversed Designs--Sequence of Printing--
Printing Inks--Purity of Tone--Drying.
Tin-plate printing or decoration is probably the most remarkable
development of modern lithography. From a most unpretentious and
unpromising beginning its evolution has been an unbroken record of
phenomenal progress. Owing to its intrinsic merits and peculiarly
assertive character it has created an enormous demand for its own
productions.
Difficulties innumerable were encountered and surmounted, whilst a whole
host of trade prejudices had to be removed before anything approaching a
commercial success could be claimed. The original idea was to transfer a
printed design from a suitably prepared paper to the metal plates in
much the same manner as the children of to-day use transfer prints for
decorative and other purposes. Though this method is now to some extent
superseded, it is by no means obsolete. It is extensively used for
certain classes of work, and so long as the present type of direct
tin-printing machine is used this transfer method of metal decoration
will more or less be retained.
It is difficult, and in some cases impossible, to print unusually large
or exceptionally thick metal plates by the direct process. Hence the
value of Transfer Printing as a useful auxiliary process which can be
resorted to without the expense of special machinery. The ordinary
lithographic paper-printing machine, without any modification whatever,
will fulfil every requirement.
Almost any paper which has been coated with a starchy composition will
be suitable for Transfer Printing. Though not absolutely essential, it
is decidedly an advantage to use a paper which is somewhat porous, not
too hard. A brief description of the principles involved will probably
lead to a clearer understanding of the points already indicated.
The print is made on the starchy composition with which the paper is
coated, and never actually penetrates to the paper itself. This
composition, being readily soluble in water, can be transferred from its
paper base to any other surface, and will carry with it any print or
impression previously made thereupon. In theory, then, this process is
exceedingly simple, nor is it likely to present any insuperable
difficulties in practice.
One of the most important features of Transfer Printing, which affects
not only the colour sequence but the draughtsmanship, is the inversion
of the design when printed. To the printer who is accustomed to chromo
work on paper, this matter will probably offer many awkward situations.
The control over colour effects is somewhat restricted, and consequently
not only care and skill, but a certain amount of special training and
actual experience, will be necessary for the production of really
successful work. In theory the outline forme should be printed first,
but in practice it is frequently advantageous to introduce some of the
transparent tints as first printings. In the first place, such prints
rarely affect the design to any great extent as far as register or fit
is concerned. Consequently, any distortion of the paper from atmospheric
or other causes has no very serious consequences, and such distortion,
_i.e._ expansion or contraction, would be most likely to occur during
the initial printings. There is yet another and equally important
reason for this suggested modification of the colour sequence. The
light, tacky tints considerably improve the printing surface offered by
the mucilaginous coating of the paper, and the stronger inks can be
printed on it with a full body of colour yet without any tendency to
smash and smear. The lighter tints, then, are printed first, and these
are followed by the opaque colours, reds and yellows being last. The
peculiar feature of such an arrangement is that, after the first few
printings, the design becomes partly obscured, and the relative value of
different colours, together with the effect of their super-position, are
frequently questions of skilful calculation rather than visual
appreciation. Thus successful manipulation is therefore more or less the
result of careful observation and wide experience. In certain classes of
work it may, of course, be absolutely essential to ascertain the effects
of colours as they are printed. This can be done by transferring a
progressive print to a sheet of dull enamel surface paper, using gum
water as a transferring medium. In all work where specific colour
effects are required it will be advisable to make such test transfers
again and again at different stages of the work.
Concerning the printing inks themselves but little need be said. They
must be of good quality, varnishable, and of intense colouring power.
Purity of tone is requisite, not only under ordinary circumstances, but
under what may be regarded as exceptional conditions. The print, when
subsequently transferred to the metal plate, will be placed in a stove
having a temperature of 140° Fahr. Few colours remain quite unaffected
by this stoving, but with carefully selected printing inks the effect is
scarcely perceptible. It can, moreover, usually be anticipated, and to
some extent minimised, either by judicious super-position or skilful
preparation of the colours themselves before printing. The following
example will suggest a number of expedients for the preservation of tone
of colour in tin-plate decoration.
Pale blues will frequently become of a decidedly greenish _hue_ when
varnished or stoved, and this may be modified by an exaggerated
intensity of colour, even to hardness, when printing. At the same time,
it must be remembered that "blues" are seldom, if ever, affected in
_tone_. Pinks of the lighter shades, on the other hand, may suffer both
in _hue_ and _tone_. "Reds" may be mixed with a more liberal amount of
"lake" than they apparently need, and then backed up with solid masses
of "yellow" and "flesh." These will restore the bright vermilion hue,
and likewise give a greater amount of density or covering power to the
colour. Black, in the same manner, may be intensified by an underlay of
blue. As far as purity and density are concerned, the "white" printing
is by far the most important. The primary function of this printing in
tin-plate decoration is the formation of an opaque ground on the metal
plate--equivalent to the white paper. Without it the colours of a design
would lose their brilliancy and effect, for their purity and density
would be affected by the lustrous sheen of the bright metal plate.
It is a printing, then, of some, importance, and the most scrupulous
care should be exercised during its manipulation. In consequence of the
exceptional density required it is usual to repeat the "white" printing
either two or three times. The first printing especially should be made
with a smooth, well-mixed ink, which should be worked with the intention
of securing a perfectly flat and solid impression rather than a heavy
body of colour. The requisite amount of density can be obtained by the
second or third impressions.
A slight tinge of "Oriental blue" given to the "white" will improve its
appearance and counteract the discoloration produced by the varnishing
and stoving.
Another point with which the average printer is not familiar is the
unusually rapid drying of each colour. The printing inks must dry on the
surface, and not even in the slightest degree be allowed to permeate the
paper. This is, in fact, the _crux_ of the whole matter; and, assuming
that the coating of the paper is suitable and perfect, the drying cannot
be otherwise than on the surface. Dryers, preferably liquid, must be
mixed with the printing inks in liberal quantities. Here, again,
experience alone can be relied upon for guidance. Printing inks have
their peculiar characteristics, and atmospheric conditions are ever
varying. It would therefore be unwise to indicate any hard-and-fast
lines upon which to work. There is at least one danger accompanying the
use of dryers in any form which must not be overlooked. Colours may dry
too hard and present for the succeeding printings a surface similar to a
varnished sheet, which will offer no _grip_ to the printing ink, and
upon which it will probably run, and, consequently, produce a defective
impression. This is by no means an infrequent occurrence. Experience
alone can prevent it, but the remedy is as simple as it is effective.
Briskly rub each printed sheet with a pad of soft rag and a little
magnesia or French chalk. Magnesia is best. It is an almost impalpable
powder, and has no ill effect even upon the most delicate tints. This
rubbing will produce a slightly matt surface on the hard glossy ink, and
on this a good solid impression may be made without further trouble.
The printed sheets should be exposed to the air for a few hours to
accelerate drying. This may be done in any convenient manner, either by
laying them out in frames or hanging them up. A "set off" in Transfer
Printing should be sedulously avoided; not that the soiling of the back
of a sheet is of any moment, but because the matter set off on the back
of one sheet must be pulled off the face of another, and that very often
in liberal proportions.
CHAPTER XIII
TIN-PLATE PRINTING--_continued_
Direct Tin Printing--The Machine--Peculiarities of
Impression--Cylinder Covering--Colour Sequence--Printing
Inks--Drying Racks--Air Drying and Stoving.
"Direct tin printing" is not, as the term might suggest, a _direct_
impression of the printing forme on the metal plate. It is in reality a
transfer printing process in which the transferring medium is a cylinder
with an elastic covering. This additional cylinder is one of the chief
characteristics of a direct tin-printing machine, and, apart from a few
accessory movements, it is in this respect alone that it differs from an
ordinary lithographic printing machine. Fig. 25 gives a sufficiently
clear idea of this distinguishing feature. A detailed description of its
mechanical principles is unnecessary, but the following points will
prove helpful.
The impression is made from the printing forme upon the lower cylinder
during the first half of its revolution, and transferred to the metal
plate, which is carried by the upper cylinder as the revolution is
completed. The reciprocal movement of these two cylinders is therefore a
matter which demands the keenest possible attention. Their pitch must be
absolutely accurate, the pressure of one against the other nicely
adjusted, and the brake arrangement on both such as to ensure a
perfectly steady revolution.
The lower cylinder is covered with a three-ply rubber blanket, which
provides a sufficiently elastic impression surface.
[Illustration: FIG. 25.--Rapid tin-plate printing press.]
This rubber covering is a most important feature, and requires both
careful adjustment and intelligent use. Careful adjustment is requisite
to ensure the tension being perfectly uniform over the whole surface,
when the material is drawn taut by means of a tooth-and-ratchet
arrangement. Were it not so, the printing surface presented would
naturally vary in thickness and resilience, in consequence of which the
pressure would be variable and the impression distorted.
A most remarkable peculiarity of this rubber covering is that it has a
very decided influence upon the size of the impression. If, for example,
its pressure upon the printing forme is increased, the impression will
be slightly less than the work on the stone, whilst a lighter pressure
will of course produce the opposite effect. It is advisable, therefore,
when making a first impression, to measure it from back to front and
compare it with the printing forme. This method will ensure a print of
the exact size, and avoid any risk of complications in the subsequent
printings. Such distortion--for a distortion it really is--may
frequently be turned to good account, and under certain conditions it
may prove to be a help rather than a hindrance. Some slight inaccuracy
in the fitting of any part of the design may occasionally be corrected
by inserting patches of thin paper under the cylinder covering, so as to
almost imperceptibly increase the pressure over the required area. This
idea in its application to "making ready" at a tin-printing machine will
suggest many possibilities to the resourceful printer, and if
intelligently treated will rarely prove troublesome. In a lesser degree
the same system of packing may be applied to the upper cylinder, and the
size of the impression to some extent controlled during its transference
to the metal plate. The speed of the machine also affects the
impression, and in a somewhat peculiar manner. Several theories have
been set forth to prove why an increase in speed should produce a
slight enlargement of the impression, and _vice versâ_; but it is
doubtful if any of them are altogether satisfactory. Most probably it is
due to a momentary change in the resilience of the rubber. The character
of the pressure, which is certainly influenced by increasing or
diminishing the speed, would of course effect such a change. The effect,
as just indicated, is, however, only perceptible when a very pronounced
variation in the speed takes place. A rubber blanket is also affected in
a somewhat similar manner by atmospheric changes, though not appreciably
by moisture.
One other point in connection with the cylinder covering is worth
noting. Whenever it is necessary to remove the impression from the
blanket,--and the necessity may arise many times during the course of a
day's run,--let it be done with turpentine or benzole, and as rapidly as
possible. After the superfluous turpentine or other cleanser has been
wiped off, dust over the blanket with French chalk. This will completely
absorb any of the cleanser which may have permeated the rubber, and thus
minimise any injurious effect.
Unlike the Transfer Process in Direct Printing, the colour sequence is
practically the same as for paper printing. There are, of course,
essential points of difference, and these may fitly mark the next stage
of progress in the discussion of this subject. In the first place, a
bright metal plate does not present an altogether suitable printing
surface, and for several reasons. The sheen of such a plate will show
through many of the printed colours with a dull metallic lustre. The
surface, again, is hard and excessively smooth, or, as it is sometimes
expressively described, without _tooth_. As can easily be seen, this is
far from an ideal printing surface.
White also plays a prominent and effective part in many designs, and is
frequently indispensable. Its presence, when necessary in Direct Tin
Printing, must therefore be arranged for in some form or other. One
white printing is seldom sufficient to produce a perfectly clean and
solid ground. Two printings, or even three, may be necessary. Purity of
tone is a most important point, and therefore a pigment should be chosen
which will not only remain unchanged by its contact with the metal, but
which will be unaffected by the heat applied during stoving. The
appearance of this white may be improved by the addition of blue, as in
Transfer Printing (p. 70), and here also the smallest possible quantity
will be sufficient.
Gold Lacquer Printing is peculiar to Tin-plate Decoration, and its
advent indicated a vast progress in artistic display and effect.
Printing lacquer is a transparent pigment of about the same consistency
and character as printing ink. It is usually prepared in three shades of
colour--red, citron or orange, and pale gold. A combination of these in
suitable proportions will produce almost any strength or shade of gold
which may be required. Except as regards their unusually brilliant
transparency, these lacquers much resemble yellow lakes, and in paper
printing might even be used as economical substitutes for the more
expensive pigments. This, however, is only a suggestion, and has little
if any practical bearing upon their application to Tin-plate Printing,
where they completely transform the bright sheen of the highly polished
metal plate into a brilliant and most effective gold. Gold lacquer is an
exceptional pigment in many respects. It works exceedingly well, and
gives a sharp, flat impression where most other pigments would fail. It
also has the power of conveying many of its own good qualities to any
printing ink with which it may be incorporated.
In Transfer Printing the question of rapid drying is very important, and
in Direct Tin Printing it is even more so. Arrangements of a somewhat
extensive character must be made for the reception of metal plates
immediately after printing, so that the air may freely circulate about
them, and thus assist in the drying. The room in which the printing
sheets are thus stored must be free from dust, for it will readily
adhere to the tacky printing ink, and afterwards prove a source of
endless trouble.
[Illustration: FIG. 26.]
Drying racks of various descriptions are used for the storage of printed
metal plates. One of the best is constructed on the lines shown in Fig.
26. The shelves A A are adjustable so as to carry plates of different
sizes. The printed sheets are set up on end in the grooves B B, and by
arranging them back to back in pairs a large number can be accommodated
without hindering the drying. Other types of drying racks are shown in
the sectional drawings (Figs. 27A and 27B).
[Illustration: FIG. 27A.]
The question of air-drying _versus_ stoving has ever been a contentious
one, and admits of considerable diversity of opinion. Air-drying _is_
preferable where convenient. It is much more economical than stoving, of
course; but, on the other hand, it might be a better plan to stove a
printing than to wait, perhaps for some hours, until it dried naturally.
With some printing inks and under certain climatic conditions both may
be necessary, so it is almost impossible to lay down any hard-and-fast
rules as to the adoption of either plan.
[Illustration: FIG. 27B.]
Some knowledge of their respective disadvantage should be acquired,
however, in order to avoid, or at least minimise, them.
[Illustration: FIG. 28.--Convenient method of stacking decorated metal
plates to distribute their weights and prevent injury.]
Take, for instance, a course of eight printings, each one absolutely
necessary to the design, and each one to be dried by stoving. It is only
reasonable to suppose that the first and second printings will be
seriously affected by the subsequent stovings. They will undoubtedly
harden to such an extent as to render the super-position of other
colours a difficult matter, and their purity of tone will most probably
be affected. According to the same line of reasoning, some sheets would
be more affected by the heat than others, owing to their position in the
racks, the heat of stoves being greatest near the top.
Air-drying can only be accomplished by adding to the printing ink a
proportion of some suitable drier. (_See_ Transfer Printing, p. 71.)
Naturally, it requires a much longer time, but it is equally effective,
much less troublesome, and generally more satisfactory.
CHAPTER XIV
TIN-PLATE DECORATION
Suitable Designs--A Variety of Effects--Gold Lacquer--
Super-position of Colours--Embossed Effects--Embossing
Plates--Lacquers.
It is usually and rightly supposed that the most effective results in
Tin-plate Decoration are produced from designs which are lithographed
for that specific purpose.
Designs which are specially arranged for Paper Printing can be used so
long as the effect produced by the transposition from right to left does
not affect its application, or render the same impossible. This, of
course, applies more particularly to designs in which lettering appears,
but at the same time it may affect designs of an essentially pictorial
character in an equally important manner; for it must be remembered that
a drawing for Tin-plate Printing must appear on the lithographic stone
exactly as it is impressed on the metal, and not, as in Paper Printing,
reversed from right to left. This naturally simplifies the drawing on
stone, and to some extent enables the draughtsman to dispense with the
reversing mirror when copying.
The primary object of this short chapter will be to point out some of
the characteristic features of Tin-plate Decoration, so that such
methods as are usually adopted by the artist and the printer may be
modified or amplified to meet any peculiar requirements of work in hand.
A greater variety of effects can be attained on the polished metal
plate than it is at all possible to produce on paper.
A gold effect, the result of lacquer printing, is especially striking.
In a similar manner an excellent translucent lustre can be imparted to
almost any colour by taking away the white opaque ground, and thereby
producing a peculiar semi-transparency which is both pleasing and
effective. Lacquer printed over _white_ produces a _buff_ colour, which
can be used as a second yellow or to form the base of a flesh. The
colour of the lacquer is softer and less obtrusive when printed under
instead of above the white. The super-position of colour generally, as
described in Chap. XII. page 70, is peculiar to tin-plate printing, and
suggests the advisability, if not the necessity, of a special design.
The advantages of such super-position are obvious and substantial. Under
ordinary commercial conditions it is almost impossible in tin printing
to obtain the same intensity of tones in the printed colours as in paper
printing. Some such strengthener as the super-position of suitable
colours is therefore necessary. The work of the lithographic draughtsman
is in this respect of a somewhat unusual character; but a little
intelligent consideration will render its execution on these lines
comparatively easy and satisfactory.
As already stated, yellows can be accentuated by a super-position of
lacquer, and in the same manner blues and greys add intensity to black.
Red can be strengthened by a foundation of lacquer, also flesh and
yellow, either singly or in combination. The drawing of lacquer and
white formes should receive the most careful attention. They should fit
each other accurately, even to the most minute details; for the
slightest overlapping will be revealed by the presence of a very
assertive buff colour, while any deficiency in combination will leave a
not less striking margin of bright tin exposed.
In some instances it might be an advantage to transfer one forme from
_black_ to _white_ to produce the opposite colour, and thus ensure
perfect register.
In decorative designs particularly, tin-plate printing suggests almost
unlimited possibilities for brilliant effects, and in this respect it
offers fair latitude for individual originality and manipulative skill.
In the production of show tablets especially, considerable attention has
been given to embossing, in order to suggest and represent relief.
Though not actually produced by the artist, this is in effect part of
the scheme or plan of his design, and will consequently influence his
work to some extent. For simple ornamentation only, metal embossing
presents little that is new or novel; but for the production of relief
effects in the pictorial elements of a design its application becomes a
more important and influential matter. By its aid a flat and otherwise
uninteresting subject can be made attractive and vigorous, and for
general purposes of effective display its value will be considerably
enhanced and its assertive character emphasised.
Without entering too minutely into matters which affect the lithographic
printer in an indirect fashion only, it will yet be useful to him to
know how an embossing die is produced which registers accurately with
the design to be operated on. A black impression of the outline forme of
the design is made on transfer paper similar to that described in Chap.
XII. page 68, and re-transferred, by pressure only, to another sheet of
the same paper. The re-transfer is to be the impression required, and
this in its turn is re-transferred again to a prepared brass plate. The
only preparation necessary is the levelling and planing of the plate,
and, if desired, it can be coated with a thin layer of white paint or
enamel. This white ground makes the work easier, by rendering the
impression more distinct. With such a guide as this the cutting or
engraving is a comparatively simple matter.
The engraved plate is placed in a casting box, and a stereo-metal
casting is made from it. A little trimming may be necessary for the
completion of these two tools, and they will require to be suitably
mounted, so that they may be accurately adjusted in the embossing press.
Metal embossing has certain limitations which must be recognised as an
essential condition of its effective application.
The plates vary considerably in texture and temper, and the depth and
character of relief will, to some extent at least, be controlled by the
quality of the metal. Sharp lines and abrupt terminations impose a
strain under which many plates split, therefore such features ought to
be avoided. Easy, rounded lines, rather than those of the straight
furrow description, produce the best results and give least trouble
during operations. Where abrupt terminations are quite unavoidable the
design should, if possible, be so arranged as to evade the
super-position of colour over these parts.
Lacquer, if properly mixed and applied, is probably the toughest pigment
used by the tin printer, and is generally suitable for embossed work. It
prints an exceedingly thin layer or film on the face of the metal, which
under average conditions rarely interferes with the working of the
embossing tool.
CHAPTER XV
PHOTO-LITHOGRAPHY
Early Experiments--An Analysis--The Direct Process--
Transfer Process--Line and Half-tone--Some Difficulties--
A Natural Grain--Ink Photo-screen Effects--Essential
Features.
One of the most promising features of lithography is its co-partnership
with photography as a rapid and accurate method of reproduction. The
resources offered by this combination are very extensive. For facsimile
copying and proportionate enlargement or reduction photography stands
unrivalled, and, although in certain phases it may be somewhat
mechanical in its effects, its relation to lithography as a reproductive
art is nevertheless of an intensely practical nature, and far from
inartistic in character.
The first idea of inking up a photographic print so that it might be
transferred to the lithographic stone was suggested in the simplest
possible manner. A brief account of its inception will be instructive as
well as interesting, inasmuch as it will lead to a clearer conception of
the elementary principles involved.
During the early experiments in carbon printing it was discovered that a
gelatinous film sensitised with certain bichromates could be charged
with a coloured pigment, and a picture developed thereon. At first it
was not realised that images produced by the action of the light on such
a surface could be inked up with a greasy composition and afterwards
transferred to the lithographic stone, but it was not long before this
important point became apparent. It was found that after exposure under
the negative the transfer ink would only adhere to such portions of the
gelatinous surface as had been acted upon by the light.
Photo-lithography will best be considered under two sections, namely:--
1. The _direct_ process, in which the actual printing surface is
prepared and exposed under the negative.
2. The _transfer_ process, in which a gelatine-coated paper is
sensitised in a solution of bichromate of potassium and the photographic
print made upon it.
The _direct_ process in its application to the lithographic stone is
uncertain in its results. It is impossible to secure sufficiently close
contact between the negative and the stone, particularly when large
surfaces are under operation, and consequently the print is rarely if
ever an unqualified success. The erasure of defective work is also a
serious matter, and can only be effected by polishing and preparing the
stone again.
In the _transfer_ process absolutely close contact can be assured by the
use of the transfer paper; and should the print from any cause whatever
prove defective, another can be made immediately without any serious
loss of time or material.
The successful application of the _direct_ process to zinc and aluminium
plates is, however, an accomplished fact. The metal plate is
sufficiently elastic to adapt itself to any inequalities on the surface
of the negative. Under such conditions as these this process offers at
least one very important advantage. There is not the slightest
possibility of distortion such as might occur in the development of a
transfer. The metal plate also lends itself to easy manipulation.
_Photo-lithography_ in _line_ is simply the reproduction of line
drawings or prints in which the design is represented in black and white
with only such gradations as may be suggested by lines or dots.
_Half-tone_ photo-lithography is the reproduction of a design or copy
which has in its composition gradations of tone in the form of flat
tints.
It is sometimes described as the translation of the graduated light and
shade of the original copy into a surface which can be printed from by
mechanical means, for which purpose the ink-bearing surface is broken up
into the most minute sections, and thus forming an almost imperceptible
grain. The first attempts to reproduce the half-tones of a copy, in the
form of a grain consisting of minute dots of varying size and contiguity
according to the gradation of tone required, were made with a screen of
open textile fabric. This screen was placed between the lens and the
sensitive plate, but the results were crude and unsatisfactory.
The invention of cross-lined screens, in which the lines were cut on
glass and filled with black or other suitable colouring matter, was a
decided advancement in the half-tone photo processes.
The "screeny" effect produced by the "unvarying uniformity of grain" in
half-tone work is undoubtedly the chief drawback to its more extensive
adoption for photo-lithography. Fine etching cannot be resorted to as in
photo-engraving, neither is it possible, to emphasise effects by skilful
overlay and underlay; consequently half-tone impressions from a
lithographic stone are frequently disappointing. There are no
insurmountable obstacles to hinder the production of excellent
transfers, nor is it a difficult matter to transfer them to stone. The
trouble is, as already pointed out, the unvarying uniformity of the
grain.
This effect, or rather this lack of effect, has been to some extent
overcome by the use of a "four-line" screen in lieu of the usual
"crossed" screen, but even this is merely a _remedy_ and not a _cure_.
It has been confidently asserted that the highest degree of excellence
in photo-process work will be attained by the adoption of what may be
termed a natural grain. Several processes have been introduced which are
undoubtedly based upon collotype methods in which a reticulated grain is
produced more or less suitable for lithographic printing. Unlike the
mechanical screen grain the texture of these processes reproduces the
original copy with but little, if any, loss of expressive power. This is
indeed a feature of considerable importance, and suggests many
possibilities in the way of artistic reproduction.
To reproduce an old chalk drawing so that it might be successfully
transferred to stone and printed in the usual way, would be practically
impossible by any other process. In copying through a ruled screen many
of the delicate contrasts of light and shade would be so reduced as to
become almost valueless, consequently the print loses both in artistic
and expressive power. In contradistinction to this a natural grain
exhibits no harshness or indistinctness in the gradations of tone, and
retains its clearness and sharpness throughout the printing operation.
Reverting again to the half-tone ruled screens, it may be well to state
that small prints, being usually subjected to a closer inspection than
large ones, must be reproduced with great attention to the finer details
to ensure a certain amount of fidelity, and for this reason a screen
with fine rulings must be employed. Naturally, stronger and more
vigorous reproduction can be secured with the coarser rulings, but the
_screen_ effect will be too pronounced for close scrutiny.
There is still much to achieve in photo-lithography, and it is probably
owing to a full recognition of this fact that the progressive character
of the process is maintained. Its commercial value is undoubted, and its
successful application is chiefly a question of _how_ and _where_ it can
be most effectively introduced.
The essential features of photo-lithography are:--
1. A copy or original in which the modelling is well defined, and the
light and shade well emphasised, even to a point of slight exaggeration.
2. A _negative_ in which the whites of the original appear opaque, with
clear glass to represent the lines and solids.
3. A _print_ which can be developed or inked up with a pigment
sufficiently greasy in nature to transfer to the lithographic stone.
CHAPTER XVI
PHOTO-LITHOGRAPHY--_continued_
The Copy--Gradations of Tone--Scraper Boards--Description
and Effect--Shading Mediums--Crayon Drawings--Half-tone
Copy.
It has already been pointed out that well-defined modelling is most
desirable in the original copy. To secure this a considerable degree of
artistic perception and discretion, as well as manipulative skill, is
requisite. In photo-process work it is almost impossible to produce
artistic effects from an indifferent or unsuitable copy.
Pen-and-ink sketches and wash drawings are entirely under the control of
the artist, and characteristic effects are chiefly due to bold and
vigorous conception and skilful drawing. Few photographs are suitable
for photo-mechanical reproduction without some previous preparation.
Accentuation or modulation of the high lights and shadows will in all
probability be necessary to secure a sufficient contrast of light and
shade. The middle tints may require but little attention, unless it be
to work down any tendency to abruptness in the gradations of tone. A
bold and well-defined silver print usually copies well when clamped
between two pieces of glass to take out the grain, and photographed by
artificial light.
Scraper boards offer most remarkable possibilities for black and white
and half-tone sketches. A careful examination of Fig. 29 will serve to
demonstrate their peculiar fitness for process drawing. A light wood
pulp board forms a convenient base upon which a thick coating of white
composition is laid. Black ruled lines are printed on this surface, and
lines of a similar texture are embossed at right angles to them. Some of
the characteristic effects which can be produced on this board by the
use of the crayon and scraper are suggested by Nos. 6 and 7, Fig. 30.
No. 8 gives a stipple which is both printed and embossed. No. 9 is a
plain board upon which pen-and-scraper effects alone are produced.
Drawings in pen and ink, on Nos. 10 and 11 patterns, may be effectively
handled by a free and skilful use of the scraper. Embossed lines only
are the peculiar features of these boards, but variety of texture can be
obtained by scraping these lines into dots.
Scraper board sketches almost invariably represent a maximum of effect
with a minimum of work, and for this reason alone such an adaptable and
simple medium should soon win its way into general favour.
Their merit, however, is not confined to this one point. They provide
almost unrivalled copy for photo reproduction, and can therefore be
applied to a variety of purposes. Even a cursory glance at the scraper
board sketch on page 91 will reveal many points of interest and value
which a more careful scrutiny can scarcely fail to emphasise.
Small patches of scraper boards can be introduced into process drawings
of any description, and brilliant results be secured thereby. In such a
manner clouds, waves, foliage, and a variety of other effects can be
introduced.
Shading mediums are already well known to lithographers, yet it is
doubtful if their usefulness for the amplification of sketches or
process drawings is fully appreciated. They offer almost endless
combinations of texture and tint, and are therefore most useful and
valuable accessories in the hands of a resourceful artist.
[Illustration: FIG. 29.--Reproduction of a drawing made on Gilby &
Hermann's scraper boards.]
[Illustration: FIG. 30.--Some scraper board textures.]
Many artists favour crayon work on a grained paper, adopting a
broad sketchy treatment in liberal proportions, so that in the
subsequent reduction the freedom of the original will be toned down just
sufficiently to enhance the picturesque and artistic value. Drawings
made on scraper boards, grained papers, or by the aid of shading
mediums, are photographed and reproduced by the ordinary line method. In
making sketches for "half-tone" photo-mechanical reproduction it must be
remembered that, as far as photo-lithography is concerned, it is
impossible to accentuate effects by what is known as "fine etching" when
applied to photo-engraving. A negative for photo-process work of any
description should be absolutely perfect in every respect. The whites of
the copy in the negative should be of an absolutely opaque black,
showing clean, sharp edges, with clear glass representing the lines,
dots, etc. These are all-important factors, and their influence upon the
reproduction of the original can scarcely be over-estimated.
CHAPTER XVII
PHOTO-LITHOGRAPHY--_continued_
A Copying Table--Exposure--Illumination--Photo-litho
Transfers--The Paper--Printing--Developing--A Direct
Process.
To discuss the respective merits of the "wet" collodion, collodion
emulsion, and dry-plate processes lies beyond the province of this work,
as does also a detailed description of the operations involved.
The processes are purely photographic, and have already been presented
to the craft in various forms. It is, moreover, almost impossible to
bring within the limits of a single chapter anything approaching to a
comprehensive record of the multitudinous details upon which process
photography is based. All that can be attempted is to take one or two
outstanding features which suggest a few useful hints.
The original or copy for reproduction must be on the same optical plane
as the sensitive plate in the camera, _i.e._ they must be absolutely
parallel with each other. There are several ways of ensuring this. The
most convenient method is to use a copying table and board similar to
Fig. 31. With such an arrangement as this direct copying can be attained
through the lens, or the camera can be turned half-way round, and the
image reversed by means of a mirror or prism attachment. The chief
advantage of such an arrangement is, that the position of the camera can
be altered at will without affecting the relative positions of the plate
and copy.
[Illustration: FIG. 31.]
Correct exposure and sufficient illumination of the copy are important
factors in photographic reproductions of any kind, but they are of
infinitely greater importance when applied to photo-process
reproduction. One is, to a certain extent, dependent upon the other. The
former must of necessity be controlled by the latter; yet no amount of
exposure will compensate for defective illumination. Where artificial
light is employed the advantage of using two lights is obviously great.
Apart from the greater brilliancy and intensity of the light, the
illumination of the copy is more evenly distributed. In scraper-board
copies no shadows are thrown from the embossed dots or lines, and the
granular texture of grained papers is almost entirely eliminated.
A bichromated, gelatine paper can be obtained by coating a hard writing
paper of medium thickness with a gelatinous solution consisting of 1 oz.
of gelatine and 1 oz. of water, and afterwards sensitising it with
bichromate of potassium. It is advisable, however, to use the commercial
varieties of coated paper, and to sensitise it as it is required.
The sensitising solution can be prepared by dissolving 1 oz. of
bichromate of potassium in 20 fluid oz. of water. Add to this sufficient
ammonia to give it a bright orange tinge. Keep this solution at a
temperature of 60° Fahr., and float the paper on it for about one
minute. Pin or clip the paper to a board or squeeze it to glass, and dry
in a dark room.
Print this paper under the negative in a diffused light until the design
appears in a rich golden-brown colour, when the exposure may be regarded
as sufficient. The time allowed for such an exposure will, of course,
vary according to the quality of the negative and the intensity of the
light.
A development of the print may now be proceeded with in the following
manner.
Thin down a little transfer ink with turpentine and distribute it
evenly on a composition roller. Roll up the print until it is completely
covered with an exceedingly fine film of ink, after which allow the
turpentine to evaporate. Immerse the transfer in tepid water for about
10 minutes, and then rub it gently with a piece of cotton lint
previously soaked in water, until the superfluous ink is removed and the
design stands out clean and sharp.
The transference of the print to stone can be accomplished in the usual
lithographic manner. The chief points to be observed are, to allow
sufficient time for printing, and to ink up the transfer with the
thinnest possible film of ink.
A photo print can be made direct on the zinc or aluminium plate, and by
a slight modification of the photo-engraving process it can be developed
according to lithographic methods.
It is impossible to introduce an intermediate process without, in some
manner at least, depreciating the quality of the work. In a direct photo
print on zinc, or, in fact, on any suitable printing surface, the finer
qualities of the work are much more likely to be retained than when a
transfer print is made under the negative and afterwards transferred in
the usual manner.
Coat a finely grained zinc plate with sensitised asphalt solution and
expose it under a negative for about 4-1/2 minutes in direct sunlight,
and from 12 to 15 minutes in a diffused light. The action of light on
the asphalt solution is to render it insoluble in turpentine, so that if
a sufficiently exposed plate is immersed in pure turpentine the lines,
etc., of the design, being of course represented by clear lines in the
negative, will remain intact, while the surrounding portions will be
dissolved and washed away. After development wash the plate freely in
water, and dry it by fanning or with a pair of bellows. Let it stand for
about 10 minutes and then slightly etch it with a very weak solution of
nitric acid. Cover the work with strong, fresh gum, and dry it
thoroughly and quickly. Remove the gum and "rub up" the design with
black ink in the usual way. Wash, dry, and dust over with French chalk.
The plate can then be prepared in the manner described in Chap. XI. page
61.
THE END
INDEX
PAGE
Adjusting pressure in machine, 38
Adjusting stones in machine, 37
Air drying--tin printing, 78, 79
Alum, 27
Aluminium plates, 57
Aluminium plates--
Alterations, 62
Direct photo, 58, 85, 100
Etching, 61
Machining, 65
Printing bed, 65
Rolling up, 60
Sensitising, 99
Transferring, 59
Aluminium rotary machine, 65, 66
American printers, 53
Asphalt solution, 100
Bavarian limestone, 1, 2
Blocking out, 54, 55
Blue tinge, 70, 77
Boxwood scraper, 20
Brake cylinder, 38
Bronze printing, 49
Cam motion, 21
Canada balsam, 54
Castor oil, 28
Cause and effect, 2
Ceramic decoration, 55
Chalk drawings, 25, 26
Chemical affinity, 2
Clean stones, 3
Cohesion in printing ink, 54
Colour and design, 48
Changes, 70
Mixing, 30
Printing, 47
Registration, 48
Sequence, 48, 50, 76
Super-position, 48, 81
Transparencies, 55
Colours, standard, 55
Copperplate press, 17
Printing, 17-19
Stove, 18
Copy, photo-litho, 89
Copying table, 96
Crayon or chalk drawing, 8
Crayon work, 89, 90
Cylinder press, 21
Damping rollers, 40
Design, 24
Design, inverted, 68
Design, suitable, 80
Development, photo print, 99
Direct impression, A, 72
Discoloration, 70
Distortion, 49, 68, 75
Dryers, 71
Drying colours, 50, 71
Drying metal plates, 77, 78
Drying racks, 78, 79
Duplication of design, 30, 31
Effect of pinks and greys, 49
Effects in tin-plate printing, 81
Elastic bedding, 22, 23
Electricity, 46
Elements of lithography, 2
Embossed lines, 89
Plates, 82
Embossing dies, 82, 83
Enamelled paper, 51
Etching, 25, 26
Evolution of tin-plate printing, 67
Exposure, 99
Fine etching, 95
French chalk, 71, 76
Skins, 28
Friction glazed paper, 51
Glass muller, 6
Gold lacquer, 77, 81
Gold printing, 49
Grain, natural, 87
Graining stones, 5, 6
Grinding stones, 4-6
Gripper, 42
Gripper margins, 31
Grit, 43
Half-tone, photo-litho, 86
Halligan machine, 34-36
Hand labour and machine, 3
Lever, 21
Roller, 28
High lights, 89
Homogeneity of stones, 2
Illumination of copy, 99
Impression, 27
Impression, size of, 75
Impression, solid, 46
Inking rollers, 39
Inks, printing, 52-56
Tin-plate printing, 69-71
Transfer, 8-11
Inverted design, 68
Key formes, 27, 41
Lacquer, peculiar feature of, 83
Lacquer, tin-plate, 77
Lamp-black, 28
Leather dressing, 22
Level surfaces, 3
Levelling stones, 37
Line, photo-litho, 85
Linoleum, 23
Linseed oil, 52, 53
Litho press for copperplate, 19
Litho press, mechanical principles, 20, 21
Litho press, pressure, 20
Litho varnish, 52, 53
Magnesia, 71
Mechanical affinity, 2
Metal plates, 57
Method, 45
Modification of colour sequence, 48
Motor driving, 46
Nap roller, 28
Natural grain, 87
Negative, 88
Offsets, 27, 28
Oriental blue tinge, 70, 77
Original stones, 30
Outline forme, 48
Packing cylinder, 21
Paper, enamelled, 51
Well seasoned, 49-51
Pen and ink sketches, 89
Pen and scraper effects, 90
Photo litho--
Copy, 89
Development, 99, 100
Direct, 85
Half-tone, 86
Inception of, 84
Line, 85
Printing, 99
Transfer, 85
Transfer paper, 99
Plumbago, 22
Porosity of stones, 2
Preparation of stones, 2-7
Preparing designs, 24, 25
Pressure alterations, 43
Excessive, 37
Litho press, 20
Peculiarities, 75, 76
Printing inks, 52
Cohesion of, 54
Printing medium, 1
Proving, 29, 30
Recipes, transfer inks, 9-11
Transfer papers, 13-15
Reciprocal movement, 72
Reducing medium, 53, 54
Register lines, 29, 30
Registration, 29, 41
Registration of colour, 48
Remedy, A, 71
Re-transferring, 31
Rotary machine, printing, 65, 66
Rubber blanket, 72-75
Resilience of, 76
Scraper, 20-22
Scraper boards, 89, 90
Scratches, 5
Screen effect, 86
Screen photo, 86
Senefelder, 2
Sensitising solution, 99
Sequence of colour, 48
Set off, 71
Shading mediums, 90
Shadow, 89
Sheen of metal plate, 70
Side lay, 42
Silver print, 89
Slogger, 38
Sludge, 5
Solid oil, 53
Speed, 36, 37, 46
Speed cones, 46
Standard colours, 55
Stone-planing machine, 3, 4
Stone-polishing machine, 4, 5
Stoving tin-plates, 78
Transferred prints, 69
Substitutes for stone, 57
Suggestion, A, 49
Super-position of colours, 48
Tooth of grained stones, 7
Of metal plates, 58
Transfer inks--
Active principle of, 8, 9
Copperplate, 10, 11
Extra powerful, 11
Plate, 9
Stone to stone, 10
Writing, 9, 10
Transfer paper--
Autographic, 14
Copperplate, 14, 15
Diaphanic, 16
Grained, 15, 16
Photo-litho, 16, 99
Specific value of, 12
Stone to stone, 13
Transparent, 13, 14
Varnished, 13
Transfer printing, 55
Transferring, 32, 33, 100
Transparencies, 55
Trimming paper, 43
Tympan, 21, 22
V-shaped edge, 22
Varnish, litho, 52, 53
Vaseline, 54
Venetian red, 28
Water of Ayr stone, 25
White printing, 70, 76, 77
Zinc plates, 57
Zinc plates--
Alterations, 62
De-polishing, 58
Etching, 61
Graining, 58
Machining, 65
Photo, direct, 58, 85, 99
Printing bed, 65
Rolling up, 60
Sensitising, 99
Transferring to, 59
_Printed by_ MORRISON & GIBB LIMITED, _Edinburgh_
* * * * *
Transcriber's Notes:
Obvious punctuation errors were repaired.
Both "overestimate" and "over-estimated" appear in the original text.
The following additional corrections were made to the text:
Page 46, "therein" changed to "herein"
(are discussed herein which,)
Page 48, "superposition" changed to "super-position"
(the super-position of blues,)
Page 70, word "the" added to text
(At the same time,)
Page 102, "12" changed to "1, 2"
(Bavarian limestone, 1, 2)
Page 102, "discs" changed to "dies"
(Embossing dies, 82, 83)
Page 103, "61" changed to "51"
(Paper, enamelled, 51)
Page 104, "4" changed to "11"
(Extra powerful, 11)
Page 104, "Depolishing" changed to "De-polishing" to match text
(De-polishing, 58)
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