Collotype and Photo-lithography

by Julius Schnauss

In this method, now universally employed, success may be said to depend more particularly upon two points. (1.) The paper for the transfer. (2.) The suitability of the negative for the purpose in view. The properties and preparation of a suitable transfer paper demand a few words. It should be of substantial body, smooth and well sized; that known as bank post is usually employed in this country. Professor Husnik in his patented process proceeds as follows: 1 part of finest gelatine is swelled, and then dissolved in 24 parts of water a solution of chrome alum 1-100 in water is added, and the solution while still warm is poured into a large zinc dish heated to 34° R. by means of a petroleum or spirit lamp. Remove any scum from the surface of the solution, float the paper one sheet at a time, and suspend to dry. The sheet is floated upon the gelatine solution a second time, and once more suspended, this time by the diagonal corner to that by which it was previously hung. Prepare a solution of white of egg 1 part, water 2 parts, and on this float the paper on one side. After again drying it is ready for sensitising, for which operation prepare a bath of water 14 parts, bichromate of potassium 1 part, methylated spirits 4 parts, adding sufficient ammonia to turn the reddish solution a bright yellow. If the paper is not prepared in large quantities, but only for immediate use, the ordinary gelatine paper of commerce[Q] may be employed with advantage, if further prepared by floating upon a bath of albumen (beaten to a froth and allowed to stand) 50 parts, water 50 parts, bichromate of potassium or ammonium 7 parts (Märkl), upon which bath the paper should be floated for five minutes. This solution is subject to the disadvantage that even in the dark it will not keep for more than a day or two, therefore it must be used at once. All photo-lithographic transfer papers, after sensitising, should be used within a few hours of their preparation or their good qualities are partially sacrificed, the solubility of the albumen layer in cold water being impaired. Photo-lithographic transfer paper prepared as above described has been for some time in the market, and may be procured as an article of commerce, in an unsensitised condition; it will keep indefinitely in this state, and may be sensitised as required. The surface should not be allowed to remain in contact with the bath, neither should the immersion be lengthy, as in either case the surface of the paper would probably suffer. After drying by suspending by one corner in the dark, the chromated paper is exposed under a suitable negative—if possible to the sun—for a few minutes only; it may be examined by non-actinic light, and when the image appears brown or grey upon a yellow ground, and all details are visible, it is removed from the copying frame and entirely covered with a thin coating of transfer ink. This as purchased is much too stiff for use, and must be reduced by means of turpentine to such a consistency that it is possible to distribute an even and quite thin layer upon the surface of the print, without its penetrating to the paper. The ink should be so thin that it presents a grey, not black, appearance.

[Q] For instance, the double transfer paper as used in the carbon process.—Trans.

Those who may find it necessary, or who care to prepare their own ink, should take—chalk ink (printing) 4 parts, beeswax 10 parts, resin 7 parts, turpentine 40 parts, tallow 8 parts, Prussian blue 6 parts, ground and mixed in a paste. The chalk printing ink should be melted by gentle heat, then add the wax and resin in a molten condition, then the tallow, and lastly the Prussian blue and turpentine; on account of the inflammable nature of the latter these operations should not be conducted at an open fire. If, after prolonged keeping, this ink becomes tough, and does not readily leave the transfer paper when transferring to stone, the addition of a few drops of olive oil will restore it to a usable condition. The ink is best applied by means of a fine, dry sponge,[R] with which it should be spread on the transfer as evenly as possible, during which operation the print must be protected from actinic light; on its completion the print is placed aside to allow the turpentine to evaporate. This in a warm room will be about ten to fifteen minutes; the print is then placed in cold water, care being taken to remove any air-bubbles from its surface. After remaining for about half an hour the uppermost layer will have become sufficiently loose to allow of its removal, together with the adherent ink not forming part of the picture, upon the application of slight friction.

[R] A smooth composition roller answers equally well.—Trans.

The Development is readily effected by means of a small, fine wet sponge, or a pad of cotton wool well moistened, which is passed over the print a few times with gentle pressure; it will be found convenient during these operations to place the transfer face upwards upon a sheet of glass.

Judgment may be formed at this stage as to the suitability of the negative, and also as to the correctness or otherwise of the exposure under it of the sensitised paper; if it should have been too short the finest lines will not be firm, but appear broken or “rotten,” as it is technically termed. On the contrary, should the exposure have been too long, the spaces between the lines, which should be quite free from ink, will retain a certain amount, in attempting to remove which the transfer will be damaged.

Washing.—Exposure, inking, and development being satisfactory, the print is thoroughly washed to remove the chrome salt. Dry the transfer by means of repeated applications of blotting-paper, and it is then ready for transferring.

Transferring.—The print should retain a little moisture, but be by no means wet. It should adhere to the warmed stone to prevent any probability of it moving while passing through the press.

Transfer too Adhesive.—Should the gelatine surface, in the judgment of the operator, appear likely to prove too adhesive, it may be further dried before use, or placed for two minutes in a one per cent. solution of tannin, and again dried between blotting-paper.

Preparation of Gelatine Transfer Paper, as used in the Imperial Military Geographical Institute in Vienna, is described as follows in the “Photographic Correspondence”:—A sheet of well-sized paper is soaked in a dish of water, and when thoroughly limp is allowed to drain, and then placed on a horizontal glass plate. All air bubbles and superfluous moisture are removed by blotting-paper and a squeegee, the edges of the paper are turned up to the depth of about 2 cm., and a warm gelatine solution (1 to 30) poured upon the paper. It sets in a few minutes, and the sheets are placed upon wire gauze to dry, this operation usually occupying about two days. A day before using the gelatine paper is sensitised by immersing for three minutes in a cold bath of bichromate of potassium (1 to 15). On removal from the bath it is allowed to drain, and the gelatine side placed upon a glass plate. The back is dried with blotting-paper, and all air bubbles removed. These operations and the subsequent drying must be performed in a non-actinic light. It may occur that after these operations the sheets when dry adhere partially or wholly to the glass plate. To prevent such an occurrence it is well to wax the plate, as in the carbon process, or to apply to the surface a weak solution of ox-gall.[S] When dry the sheets are cut to the required size and printed under the negative. On removal from the printing frame they are placed in cold water until quite limp, removed, placed face upwards upon a glass plate, and surface dried with blotting-paper. Should the gelatine swell too much the sheet is placed for two minutes in a chrome-alum solution (1 to 200) and again blotted. Ordinary transfer ink, thinned with turpentine, is now thoroughly rolled up on the inking slab by means of a leather roller (as previously described in the instructions under Collotype); a fine velvet roller, lightly charged with ink, is then passed over the still moist transfer. Should the latter become dry in places it is again passed through the water bath, and the inking is again proceeded with. If the ink adhere to other parts than the design it is easily removed by the application of a damp sponge or the tip of the finger. The process of transferring to stone is as previously described. The stone itself is prepared in the manner described for the autographic process (see page 135). Damp the back of the transfer with water only, and after passing through the press several times, remove the paper from the stone; if of good quality this may be done without tearing. The transferred impression being still easily obliterated, it is better to let the stone stand for a few hours without gumming; this will allow the ink to dry deeper into it. Coat the whole of the surface with a moderately thick solution of gum, and again allow to dry. In this condition it may remain indefinitely, but under any circumstances it is advisable to allow it to remain a day before etching and printing. The gum solution used should be freshly prepared, as when old it becomes acid and acts as a mild etching medium. Remove the gum with a clean sponge previously to printing, and while the stone is evenly damp with gum solution the picture may be either rolled up with stiff chalk ink, applied by means of a leather roller, or, as preferred by many, rubbed in with a sponge containing thinned transfer ink. When the drawing appears clean and perfect the stone is washed with a wet sponge, coated with gum, placed aside to dry, and allowed to stand for a day. After the removal of the gum proceed as previously described, viz., roll up with stiffish ink, nowhere allowing the stone to become dry, and etch. This operation must be conducted with care and judgment, or there will be a probability of losing the finer lines of the drawing. The best mordant to use is nitric acid, so dilute as to taste no stronger than lemon juice, and which, placed upon the edge of the stone for a few seconds, will show only slight effervescence. To this is added a little gum-water, and it is then evenly and quickly spread over the stone. After being allowed to act a few seconds, the stone is sponged over with clean water, and is then ready for printing from.[T] There are many practical lithographers who prefer to entirely remove the visible image from the stone by means of turpentine before printing. A little gum is left upon the stone, and while the latter is still moist the drawing is removed by means of turpentine upon a piece of rag; the latter must not be too frequently changed, or a too liberal supply of turpentine made use of, or the drawing may be irreparably damaged. Unless the latter be the case the picture will reappear upon applying the roller charged with chalk ink. As may be expected, the first few impressions are seldom so perfect as the later productions. After each impression is removed the stone is at once slightly moistened. For this purpose a soft, clean sponge is suitable, or damping cloth, as supplied by dealers in printing materials. The sponge or cloth should be thoroughly wetted, wrung as dry as possible, and in that condition will possess the necessary dampness. In rolling it should be borne in mind that as in Collotype a stronger grip of the roller handles and heavy pressure with slow rolling will deposit ink upon the drawing—while, on the other hand, light quick rolling of the drawing will tend to remove the ink. To leave the stone without gumming after transferring is a convenient method of rendering the transfer more receptive of the ink. In lithographic as compared with Collotype printing the ink is reduced to a far greater extent with varnish, while both the inking slab and roller are charged far more heavily. The paper may be damp, or a dry, well-sized paper may be used.