Part 3 (1/2)
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 a.s.sociated 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 cla.s.s 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 sc.u.m 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 was.h.i.+ng 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 pa.s.sed 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 pa.s.s 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 const.i.tute 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.
[Ill.u.s.tration: 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 sc.r.a.ping 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, pa.s.sing 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.
[Ill.u.s.tration: FIG. 10A.]
[Ill.u.s.tration: FIG. 10B.]