Among the many published formulae for photographing on wood, nearly all are defective at one vital point; that is, the block becomes wet during the operation. In this respect, engravers' boxwood is peculiar, and to wet a block is generally to spoil it. In preparation, the logs are sawn transversely into wheels about 1 in. thick, and planed down to type height. As the trees are of comparatively small diameters, it is often necessary to glue several pieces together to obtain a block of a given size. To salt and sensitise a block in the usual way wets it, of course, and the final toning and fixing gets it thoroughly soaked. The surface on which the engraver works is endwise the grain of the wood, the pores of the wood running straight through. Water quickly penetrates these pores, thereby causing the block to swell and warp, and, when subsequently dried, it very often does not regain its former level condition, which is essential. The small pieces composing the whole often expand unequally, thereby tearing them apart at the joints. Besides this, the glue in the joints becomes softened, making it liable to break in the press. The mere sensitising of the surface will often cause the block to warp so much that it is impossible to get good contact in the printing frame.
Rinsed negatives are required also, which is another trouble.
There are 2 ways of printing on wood which give good results, and do not damage the block in the least. (1) From a negative of the subject desired, make a clear, thin positive on glass, by the wet collodion process. The positive should be of the proper size, on clean glass, without the substratum. Tone and fix as a transparency, and lay in a dish of water containing a small percentage of sulphuric acid, to loosen the film. The film will soon become so loose that it can be easily stripped from the glass and transferred to the block. To do this safely, lay on the film a piece of wet albumenised paper a little larger than the glass. Press out the bubbles and surplus water carefully, then turn back one corner of the paper, and it will come off, bringing the film with it. Have the block smoothly whitened with Chinese white in gum-water, and the surface slightly damp. It is now easy to transfer the film to the wood and remove the paper, when the block must be allowed to dry spontaneously.
(2) Another way to print on wood is by a sort of photo-lithograph process. Coat paper with a thin, uniform coat of gelatine in Warm water. Dry, and float a short time on a weak solution of potash bichromate in water. Dry again, and expose under a negative till all the details are visible. Roll the entire surface of the print with a printers' roller charged with lithographic transfer ink thinned with spirits of turpentine. Soak the paper in a dish of tepid or warm water until the ink can be removed by rubbing gently with a soft sponge. All the ink, except the lines composing the picture, can be removed, when the print should be laid face down on the whitened block, and subjected to a heavy pressure in a common letterpress. The paper can be easily removed by wetting the back.
(3) Another application of photography as a help to the engraver was discovered by the writer. Procure hard rubber, in smooth, black, polished sheets about 1/8 in. thick. These are to be cut to the proper size, cleaned, and albumenised the same as glass for negatives. The rubber-plate is covered with collodion, sensitised in the bath, exposed in the camera, and developed in the usual way of making a negative. In fact, the whole operation is exactly the same as in making a ferrotype, on rubber instead of an iron plate, and a ferrotype bath and collodion are well adapted to the rubber. When a clean, sharp image is obtained, it is fixed in cyanide, varnished with a thin transparent varnish, and dried by a gentle heat. The plate is now ready for the engraver, who will have a fine smooth surface and a clean drawing to work on. (T. C. Harris.)
(4) The following method, by which F. E. Ives says he has put hundreds of photographs on wood for engravers, gives better satisfaction than any he has seen published. Notwithstanding the considerable amount of wetting which the block receives, there is never any complaint of injury therefrom, unless the blocks are very green.
is whitened by putting on 2 or 3 drops of thick salted albumen, then sprinkling on a little pure dry white-lead (zinc white must not be used), and spreading and mixing them with the ball of the hand until the coating is thin, even, and smooth. Rub from the middle of the block, with alternate strokes to the right and to the left, occasionally turning the block to make the strokes crosswise, until the coating is so nearly dry that the "last gentle strokes serve to smooth it almost to a polish. It requires some skill to perform this operation successfully, and it cannot be well described. If rightly done, the coating will be thick enough to make a bright print, but will not chip or give any kind of trouble to the engraver, not even for the very finest work. The correct amount of albumen and white-lead, as well as the proportion of one to the other, must be learned by experience, and will be found not to be the same for all blocks.
When the coating is perfectly dry, it may be polished with a brush, then sensitised by covering the surface for exactly 2 minutes with a 60-gr. solution of silver nitrate. Rub off with a blotter, and when perfectly dry, fume 20 minutes with ammonia. After printing (under a reversed negative), wash with running water not more than 3D seconds, and then tone and fix at once by placing face down upon a solution of soda hyposulphite (1 to 6), to which has been added a pinch of soda carbonate and a little gold chloride; 20 minutes' fixing is right, after which the block is washed, and allowed to dry, when it is ready for the engraver.
The salted albumen is made by adding 80 gr. ammonium chloride to the well-beaten white of 6 fresh eggs; a few drops of ammonia may be added, but no water. Blocks which are white and porous from over-seasoning must be coated twice with the albumen, the first application to fill up the pores of the wood, and the second (after the first has dried in) to prepare the surface. The thick albumen rubbed into the face of the block, and then coagulated by the silver nitrate, preserves the wood from injury. In skilful hands, the method is quick and reliable, and the results are very satisfactory.