CHAPTER VIII.
Printing in the Press.
THE etching or damping and rolling-up of the Collotype plate presents difficulties which are greater even than those met with in the preparation of the plate. These remarks also apply with equal force in photo-lithography, and whoever stops at the preparation of the plates or the photo-lithographic transfer, and leaves the subsequent operations to be performed by another, should not be considered either as a collotypist or photo-lithographer. The whole success depends upon a succession of apparent trifles; many errors it is impossible, or at any rate difficult, to rectify, and great care should be taken that nothing is overlooked, or from some trivial cause the whole may result in failure.
Firstly, remove all adherent matter from the back of the plate, as the smallest amount of dried gelatine, particle of grit or other hard matter will suffice to cause the fracture of the strongest glass plate on the first application of pressure.
The Etching or Damping Solution in most common use consists of a stock solution of five parts water, one part liquid ammonia, three parts glycerine, and one-tenth part of nitrate of lime. For use add five or six parts of this solution to 100 parts of water, sufficient of this being used to well cover the plate when placed in a clean dish. Another reliable formula is one litre glycerine, 600 cc. water, chloride of sodium three grammes. Plates may be immersed in these solutions for a time extending from ten minutes to five hours, or they may be well flooded with it, wiped off, and dried with blotting paper.
The press having been examined, oiled, and put in thorough working order, the next consideration will be
Fixing the Collotype Plate, which may be performed in several ways. Immersing the plate in the etching fluid precludes the old method of cementing it on with plaster of Paris, or glue and whitening, but it may be fixed by adhesion to a bed of glass or a polished iron plate, or a special and somewhat complicated frame may be procured for securing the thick printing plate by means of adjustable clips secured by screws. Should the printing surface be upon a thin glass adhesion alone will be found sufficient, a few drops of water causing the printing plate to adhere to the thicker glass plate underneath. This method has the disadvantage that it is most difficult to ensure the position of the plate being in keeping with the mask on the frame. Should the mask be placed directly upon the gelatine surface of the plate it will not last many impressions without either tearing or causing damage to the surface through the formation of creases or wrinkles. If the picture has to be trimmed without margin, and mounted—either with or without varnish—the masking is altogether unnecessary. The preparation of the ink and rollers should next be proceeded with. Supposing the work in hand to be one of a simple character—say the reproduction of an impression from a copperplate in black—take a piece of the best chalk ink about the size of a hazel nut, in an unthinned condition, as supplied to the printing trade, and with an iron spatula or palette knife spread it upon the inking slab. Add one-quarter the amount of middle varnish (refined and odourless), one drop of olive oil, and one or two drops of best French turpentine, incorporate thoroughly by means of the palette knife, divide, and apply one-half to the roller. The next operation is the important one of
Distributing the Ink.—A really good leather roller, the handles of which should be encased with easy fitting leather covers, is most suitable for the purpose. The ink, by careful manipulation of the roller, should be gradually distributed over the entire surface of both roller and slab in a perfectly even and regular manner. Should any small lumps be observable upon either surface they should be carefully removed with the palette knife and the rolling and distributing again proceeded with, as on careful attention to this matter the excellence of the resulting print greatly depends. The printing plate being well secured, its moistened surface should be very evenly dried. This is best effected by means of a roller covered either with fine cloth or washleather, or a fine soft linen cloth may be used as a substitute.
Rolling up.—Apply the inking roller with light pressure to the nearest edge of the plate, and roll backwards and forwards over its surface several times; an experienced printer will at once perceive the condition of the surface. For the first inking a stiffish ink should be used, as the plate will not then so readily become dirty. By repeated rolling in different directions, and what is of equal importance, with varying pressure, endeavour to distribute the ink with perfect evenness, and with a view of producing a clear and vigorous inking, which will yield a similar perfect impression. It should be remembered that