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
1. A slow rolling with heavy pressure deposits ink on the plate; and
2. Light and quick rolling removes the ink from the print layer.
By modifying the treatment of the plate, and varying the application of the roller and damping solution, an experienced printer will demonstrate his power of producing from the same plate flat, weak, and unsatisfactory impressions, or prints as clear and vigorous as may be desired. The first application of the ink having been made with a leather roller, it should be distributed, and the half-tones improved by the application of a smooth roller, preferably of glue composition. Without this second inking, it will be found impossible to produce the highest results in half-tone.
The Second, or Composition Roller, must be lightly charged with ink considerably thinner than that applied in the first instance, the remarks concerning the pressure applied to the leather roller applying with equal force in this case. By light, quick rolling, the ink is partially removed from the plate, while heavier pressure and slower movement will deposit ink and strengthen the shadows.
When the inking is complete, the frame with the mask is placed in position. The printing paper, which may be either strong, well-sized letter-paper, thin cardboard, or the paper known in the trade as “dull enamel,” cut to a suitable size, is adjusted over the mask, and backed with a couple of thicknesses of smooth paper. This again is covered, with the tympan attached to its frame. Push the bed of the press so far under the scraper that the latter, when pressure is applied, will nip the plate about one centimetre from the commencement of the picture. This position has to be ascertained by trial before covering with the second or tympan frame.
The Scraper being regulated so that it will give a sufficient pressure, pass the bed quickly through the press to the extent necessary to produce a complete impression. The length of traverse of the bed during printing can on most presses be regulated by side screws, or the tympan may be lightly marked. After releasing the pressure, the bed is withdrawn, the tympan and masking frames thrown back, and the printing paper cautiously raised by one corner. It often adheres slightly to the printing surface, and this is usually an indication of a good plate. The adhesion may, however, at times be so strong as to tear the paper, or, in the case of enamel paper, remove the chalk coating. As previously mentioned, the scraper should be selected of a width somewhat exceeding that of the picture, but never exceeding that of the glass plate. It may be left plain and moderately sharp, or covered with leather.
Damping the Plate between each impression will usually be unnecessary, providing a good sample of gelatine is used, and the damping solution contain a sufficient quantity of glycerine. In cases where the Collotype plate has been over exposed, or the subject be one which requires an absolutely white background, damping between each impression will be absolutely essential. Where it is omitted for any length of time, the whites of the pictures will always be more or less degraded or tinted. Should the early impressions not be satisfactory, patience should be exercised, and by careful treatment with the roller or rollers, and care in the damping, favourable results will often ensue after the first few impressions have been pulled. Only from actual damage to the print layer, or excessive over exposure in the copying frame, need the plate be placed aside as in a hopeless condition. The beginner should guard particularly against mechanical damages in damping; drying and rolling. Lithographers are inclined to treat the delicate printing surface with the same vigour and energy that they would apply to the more substantial lithographic stone to which they are accustomed.
The following directions from “Kleffel’s Manual of Photography” are to be recommended in printing line subjects, particularly in “glass” printing direct from the negative:—“The chromated layer of gelatine must have been submitted to a sufficiently long exposure to ensure it taking the ink over the whole surface. For the first rolling in of the plate, the ink should be composed as follows: White wax, 45 parts; middle varnish, 5 parts; gum elemi, 15 parts; litho ink (about 5s. per lb.), 20 parts.
“After the plate has been thoroughly rolled in and blackened, it must be rubbed with a piece of unbleached muslin, previously saturated with the following solution: 30 parts of ammonia and oxgall (about equal parts), 30 parts gum arabic, 90 parts water, until the picture develops perfectly clear. Dry with a clean piece of muslin, and roll in for the printing proper with ordinary thin copper plate printing ink. Plate paper, similar to that used in printing from the copper plate, is most suitable.”
When printing operations are complete, the rollers, printing plates, and inking slabs should be at once cleaned, as the varnish colours soon harden and create difficulties.
Cleaning Leather Rollers without damaging them requires considerable practice. They are always scraped with a clean knife, and the operation should be performed in one direction, to ensure which it is advisable to mark one of the roller handles. Leather rollers not in constant use, before being put aside, should have their surfaces carefully and thoroughly rubbed over with tallow, which must, of course, be scraped off before the roller is again used.
Cleaning Composition and Indiarubber Rollers should not be effected by means of scraping, but their surfaces should be cleaned with turpentine, applied with a linen rag free from lint.
Cleaning the Plates.—Turpentine is used to free the surface from every particle of ink, and after the thorough evaporation of the spirit, the plates should be well washed in water to remove all trace of the damping solution, dried, and stored in a cool place. It is sometimes a matter of difficulty to remove ink from Collotype plates that have been printed from, but a simple method is to pour over the plate—as in developing a collodion picture—some lukewarm water. This will dissolve a thin layer of gelatine, and enable one to at once proceed with the work.
CHAPTER IX.
Finishing and Varnishing Collotype Prints.
RETOUCHING Prints.—Under the above heading Leon Vidal, in his work “Traité Pratique le Phototypie,” gives the following directions, which I reproduce from the “Photographic Archives.” Even with the utmost possible care in the preparation of the printing surfaces there will be required in most impressions a little retouching, if only to hide a few white spots. In large orders this cannot be carried to the extent it is in silver prints. It happens in printing that particles of dust find their way to the plate, and cause either light or dark spots in the impressions; the former are covered by touching with ink, the latter are removed with the erasing knife, and the white spot resulting from the operation is toned down with ink. This spotting is quickly performed. The paper being dull a colour should be used containing only a small proportion of gum; it will then be invisible. Prints which it is intended to varnish should not be spotted until they have been sized, unless printed upon a paper already impervious to the varnish. The colour most suitable of all is the actual printing ink thinned with turpentine, by using which the trouble is avoided of mixing any special colour to match the tone of the impression, as the two colours are necessarily identical. Another advantage gained by adopting this method is that the spotting may be completed before sizing, as the aqueous solution of gelatine will not cause it to run. For impressions in pure black the lithographic chalk is probably the best medium for correcting proofs, as the colouring matter will be found to well harmonise with the general appearance of the picture. A blacklead pencil, on the other hand, is quite unsuited for the purpose on account of the highly metallic appearance visible wherever the pencil has been applied to the print. Retouching or spotting should not extend beyond the removal of light and dark spots; the correction of larger faults should not be entertained, but a fresh printing surface produced. Faults present in the original negative should be carefully retouched and removed or reduced as far as possible. Should the white margins of the picture become soiled by contact with the inky mask or by finger marks, they may be cleaned with indiarubber ink eraser. The backs of impressions may also be cleaned in the same manner.
When copies have to be mounted on cardboard they may be either left with a matt surface or varnished. In the first case, the edges are trimmed, and they are then mounted upon the cardboard mounts. If the latter have been previously damped they will retain their flatness.
Rolling or Burnishing must not be done until the prints have completely dried, or the picture may be torn from the mount.
Sizing and Varnishing.—Prints to be varnished may be printed on prepared or sized paper, and in such cases may be at once varnished. If, on the contrary, the paper is not sized, they require a special preparation, as follows:—A 10 per cent. solution of gelatine is laid on with a broad camel-hair brush, avoiding air bubbles and streaks. After a little practice this operation will be found both easy and rapid. The sized pictures are pinned in pairs back to back on a wooden frame, to which strips of cork are attached; when the prints are quite dry the operation of varnishing may be proceeded with. A good varnish, probably the best for the purpose, which possesses the double advantage of remaining colourless and setting very hard, consists of a solution of 15 parts of white (bleached) lac in 100 parts of wood spirit (vegetable or wood naphtha). On dissolving the shellac it will be found that the solution is clouded on account of the suspended fatty matter, the removal of which is always desirable; the varnish will then filter more rapidly and give a more glossy coating. By adding powdered lime three parts of the solution may be decanted clear, and the remainder may also be used after filtration through felt. Or if to three parts of varnish one part of benzine or petroleum ether be added, the solution will resolve itself into two layers, and the upper one, which will contain the fatty matter, may be poured off. The varnish is best applied by means of a ball or dabber, care being exercised to avoid air bubbles; the print is next placed in
The Drying-box (see fig. 8), which is a four-sided tin box 1 m. long by 0·25 m. high. A gas-pipe, perforated with small holes drilled about 6 to 8 cm. apart, runs through the upper part of the box, the front of which is open to two-thirds its height. A plate, finely perforated, divides the upper third from the lower two-thirds, and forms an inner division, through the upper of which the gas-pipe passes. The flat perforated division is hinged to allow of being opened for the purpose of igniting the gas. The pictures placed on the bottom of the box dry very rapidly, while the perforated division prevents the possibility of the ignition of the vapour of the spirit employed. With such an apparatus it is possible to varnish and dry a large number of prints in a very short time.
Fig. 8.
Sizing may be Avoided if each picture, after well drying, be dipped into the following solution: Water 500 g., borax 130 g., white shellac 100 g., carbonate of soda 6g. The borax and carbonate of soda are dissolved in boiling water, and the powdered shellac then added in small quantities; when solution is complete carefully filter and allow to cool. The impressions, two and two, back to back, are pinned on frames, dipped in the varnish, and afterwards dried. By this procedure a shellac coating is given to the surface only of the print; there is no gelatine substratum to soften through atmospheric influences, and so crack and destroy the layer of varnish. In winter the temperature must be kept high, and the solution should be heated 15° to 20° C.
Parchmentising to a slight degree may also be adopted to close the pores of the paper. Add one part by volume of water to two parts of sulphuric acid, allow it to become quite cold, immerse the pictures for one second only, and at once wash in a copious supply of clean water to which has been added a small quantity of ammonia to effectually neutralise the acid. The action of the acid must not be carried too far, as it is merely necessary to act on the surface. To prevent paper so treated from cockling while drying, it must be put under pressure or stretched upon a frame; when quite dry it has to be varnished and dried by heat.
Varnishing Enamel Paper without previous sizing is best done by means of an alkaline solution of shellac prepared as follows: Place in a six litre tin flask 1/2 kilo of bleached and powdered shellac, pour over it 1-1/2 kilo of alcohol and 1-1/4 kilo of strongest ammonia. In the course of a few days the solution of the shellac will be complete, then add, with constant stirring, 2-1/2 kilo of hot water, and when cold filter. It may be applied to the print with a broad Blanchard brush,[K] and left to dry in a horizontal position. The prints may also be floated on the varnish for about half a minute, and then suspended to dry by means of clips. After a few minutes have elapsed a piece of blotting paper should be applied to the bottom edge to absorb the superfluous varnish.
[K] Made as follows: Take a piece of glass, say 20 cm. long by 6 or 7 cm. wide, and a piece of swansdown calico the same width as the glass but only 6 cm. long, fold this over the one end of the glass, 3 cm. being on each side, and bind round with thread or spring on a rubber band.
Rolling or Burnishing must on no account be attempted until the mounted prints are perfectly dry, otherwise they may be seriously damaged or even completely torn from the mounts.
CHAPTER X.
Other Collotype Processes.
THE Artotype Company, of New York, which has acquired Obernetter’s process, proceed on somewhat different lines to those laid down in this work, and an abstract of their proceedings is here given as interesting to those about to experiment. According to Bachrach, “Photographic Archives, 1879,” p. 66, they proceed as follows:—
Fig. 9.
Plates coated with Husnik’s silicate of soda substratum are dried rapidly in a box heated to 65° C. This causes the solution to coagulate, the plates are dried in half-an-hour, and as it adheres with great tenacity to the glass plate, the latter may be at once coated with the chromated gelatine solution, or it may be kept till the next day. Before the second coating is applied the plate is well washed and allowed to dry spontaneously. The drying-box is of wood, 2-1/2 feet square and 5 feet high, the entire front being a large door, as shown in the sketch (fig. 9), and the bottom a flat water tank about four inches deep fitted with two pipes, one to allow the escape of steam, and the other of use in filling the tank with water. It may be heated by means of gas or a petroleum lamp. After the bottom of the box has been accurately levelled, it is covered with a few sheets of blotting paper, on which are placed the albumenised plates. Occupying the upper part of the box are adjustable racks, on which other plates are dried. The box is heated to 82° C., the plates are levelled in their places, and just sufficient hot chromatised gelatine solution poured on each to spread up to the edges—not more. The Artotype Co. takes one-third each of gelatine, isinglass, and the so-called Magdebourg isinglass. Plates are allowed to remain in the drying-box about 20 to 30 minutes, during which time the door must not be opened, and particular importance is attached to the high temperature, reaching even to 93° C., at which the drying is completed, as it is considered by these means printing plates of much finer grain are obtained. (The Author believes the temperature given is much too high, as it would be sufficient, without exposure to light, to bring about a partial decomposition.) When dry, the plates may at once be printed under the negative. To etch the plate it is immersed in a solution of 5 gr. alum in 1 litre of water, rinsed, allowed to dry, and put in a bath consisting of 150 ccm. of water, 1 litre of glycerine, 300 ccm. of ammonia, 30 g. nitrate of lime. Plates that have been exposed under the negative too long are treated with a solution of 20 parts of ammonia, 20 parts of glycerine, and one part of Venetian turpentine; with this they are flooded. The remainder of the process is very similar to that already described.
Seignior Carlos Relvas.—Vidal publishes the following method of procedure as that adopted in the studio of this eminent Portuguese amateur collotypist, where it was introduced by Jacobi:—Very thick glass plates, finely ground on one side, are used; they are cleaned with nitric acid, and rinsed in distilled water. The drying box used is provided with iron bars, fitted with adjustable screws for the purpose of accurately levelling the plates. Midway between the top and bottom of the box is an iron plate, underneath which are fitted gas jets. The doors by which access to the box is gained for the plates consists of very fine wire gauze, allowing the escape of steam, but preventing the access of insects. After a thorough cleansing, the plates are levelled on the adjusting screws, allowed to thoroughly dry, and then coated on the ground side with the following solution—
| White of egg | 160 | ccm. |
| Bichromate of potassium | 8 | g. |
| Distilled water | 480 | ccm. |
| Glycerine | 16 | drops. |
To which is added sufficient ammonia to give the liquid a pale yellow tint, somewhat less being used where a hard negative is to be employed. This substratum is filtered, and the plates afterwards coated and placed upon the levelling screws in the drying box, which is heated to a regular temperature of 40° C. In about two hours the plates will be dry, and are then placed, coated side downwards, upon a black cloth, the back of the plate being exposed to diffused light for half-an-hour. It is again placed in the drying box, and the second coating, as follows, applied—
| Gelatine | 27 | g. |
| Water | 400 | ccm. |
| Bichromate of potassium | 9 | g. |
| Preparation A | 15 | ccm. |
| Preparation B | 15 | ccm. |
| Ammonia a few drops. | ||
The preparations A and B are as follow:
| A.— | Chloride of sodium | 1 | g. |
| Water | 500 | ccm. | |
| B.— | Sulphate of alumina | 1 | g. |
| Water | 100 | ccm. |
To each square decimetre of surface should be allowed 2 ccm. of the above solution. The plates are replaced in the drying box, which is heated to 45° or 50° C. They should be dry in three hours, and are then ready for printing under a negative in the copying frame. They are afterwards well washed in filtered water, and allowed to dry spontaneously in a dust-proof situation. In two or three days the printing may be proceeded with, the surface having been softened by allowing the plate to stand for seven hours in the following solution—
| Glycerine | 500 | ccm. |
| Distilled water | 200 | ccm. |
| Preparation C | 100 | ccm. |
| Preparation C.— | Sulphate of magnesia | 50 | g. |
| Distilled water | 500 | ccm. |
All solutions are filtered through flannel. From the face of the plate the superfluous moisture should be removed with a sponge. A very thick glass plate is fixed to the face of a lithographic stone by means of glue and whiting, and adhesion is secured between the face of the thick glass plate so fixed and the back of the Collotype plate by means of a few drops of water. The whole, so arranged, is placed upon the bed of the press. Should the prints lose their contrast while the printing is in progress, they are lightly sponged over with a sponge dipped in the last-mentioned solution. If this fails to produce sufficient effect, the plate is first washed with turpentine, and then with the glycerine solution. Care should be taken to prevent the two liquids becoming mixed on the plate, to prevent which different sponges and drying cloths should be used.
CHAPTER XI.
Failures in Collotype.