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PRACTICAL LITHOGRAPHY

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

ILLUSTRATIONS

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.

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.

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:—

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:—

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:—

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:—

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:—

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:—

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.

Fig. 3.

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.

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.

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.

Fig. 5.

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].

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.

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.

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.

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.

Fig. 10a.

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 7¼ in. by 4½ in., then the paper on which it is to be printed ought to be double crown, 20 in. by 30 in. This will allow 1½ in. for the gripper and ½ 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.

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.

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.

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.

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]).

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.

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].

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.

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.

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.

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.”

Fig. 20a.—Patent conical counter shafting.

Fig. 20b.—Patent conical counter shafting.

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]).

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.