Photo-Lithography

In the first place the good quality of the stone should be looked to. For ordinary or coarsely drawn subjects this is of less importance, but for fine drawings and autotypes it is of the highest importance. Further, accuracy and cleanliness are all important, without which successful work is impossible. On the other hand, a transfer can hardly fail if it be accurately and correctly performed.

When the print comes from the developing bath, and has been well washed so that every trace of bichromate is removed, it should be freed from excess of water between blotting-paper. It should then be dried in a not too warm place free from dust till the gelatine has completely set and feels absolutely dry. The relief will have now again disappeared, and the black and white places lie in the same plane. It is best dried by pinning it to a board with drawing pins, and then set up in a dry place.

In the meanwhile the transfer stone should be prepared, which must be absolutely faultless. Just before the transfer it should be dry polished with pumice stone, and then well dusted with a {58} cloth. The slightest grain will give a spot in a fine tone. Obviously the stone must be well ground so that neither any spots nor lines of an earlier transfer can appear. With an open drawing this can be corrected, but not with an autotype; in such a case the shortest way is to make a new print and a new transfer.

The print is first wiped over on the back with a damp cloth, and then laid on damp blotting-paper. After about five minutes the print is treated a second time with a damp cloth, and then laid between damp blotting-paper. It is not advisable to lay the print between ordinary damp blotting-paper, as the gelatine becomes somewhat sticky, and would attract particles from the rough paper.

The degree of dampness which is necessary for transfer may be judged in that the print must feel soft, but the gelatine film ought not to be very sticky. Any further preparation of the print before transferring to the stone is not necessary. The print is laid on the stone, over it a dry sheet, and then the cover, and then drawn through the first time with light pressure.

In order to prove whether the transfer has taken well a corner may be lifted up. All the ink which was on the print must be transferred to the stone, and then the transfer has been completed in the correct way. The print is now pulled off the stone and the transfer made ready, like any other.

With this method of treatment the print will strip easily, which is not the case if it was not well dried after the developing bath; a much sharper and cleaner transfer will also ensue. If the print was too damp a fuzzy, broken-down transfer will be obtained, because the gelatine, which has become too soft, will be broken down.

I will also mention that it is not advisable to treat fine drawings or autotypes with the rubbing-up pad. It is better to go over the transfer with the roller, and the tones are kept cleaner. The stone is then gummed, placed on one side, and allowed to stand some hours before being etched.

For transferring to zinc plates which are to be etched or to be printed from, the bichromated gelatine print should be bathed in a ten per cent. solution of alum, allowed to dry, and then, as previously described, damped, and then transferred under the same conditions as to stone.

It only remains to mention that the stone or zinc plate should not be too cold.

The squashing down rarely happens with photo-litho transfer, because a good photo-lithographic paper will bear a considerable {59} amount of dampness. When, however, it occurs it may be assumed that either too strong pressure or insufficient care in the setting of the stone is the cause. Much more frequently it happens that some parts of the print do not transfer at all, or only in a defective manner. The chief reason of this is that the print was insufficiently damped. This frequently happens if ordinary or gravure prints are to be transferred with photo-lithographic prints. If the printer encloses the impression on the ordinary transfer paper and the photo-lithographic together in the same damp sheet, and if he estimates the degree of dampness from the gravure print, the photo-litho paper will be insufficiently damped and a good transfer will not be obtained from the latter. If, however, he waits till the photo-litho paper is damp enough, the other impressions will be too damp and will squash out in transfer. For such work the print on ordinary transfer paper and the photo-lithographic print should be kept separate, so that the different dampness requisite for each can be regulated.

Another case which frequently happens is that the print is contaminated with particles of dust or other foreign substances. These may be flying about in the air or be on the stone, the roller, or the damping paper. Through this many transfers of fine drawings are rendered useless. Perfect cleanliness of the utensils and the use of the correct ones, combined with a drying-room for the print absolutely free from dust, are absolutely essential for faultless work.

The composition of the ink, especially if it was too hard, may give rise to bad transfers.

Photo-lithographic papers, which are prepared with very hard gelatine, must be laid before transferring in lukewarm water. By this means the hard gelatine becomes rather sticky, and the greasy ink transfers much better. Even those points which in developing have taken up little ink, and appear grey, transfer completely to the stone and adhere firmly.