Read Ebook: Practical Lithography by Seymour Alfred

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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.

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 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 , 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.

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.

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.

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.

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 .

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 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.

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.

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.

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.

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 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.

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 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.

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.

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.

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.

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.

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.

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