PRINTING ON WOOD, CANVAS, OPAL, AND TRANSPARENCIES
Printing on Wood.—To print on a wood block a design to be engraved on the same presents certain difficulties. In the first place, the sensitizing solution must not be absorbed by the wood, but remain wholly on its surface; then the photo film, although thick enough to produce an image sufficiently intense to be distinctly visible in all its details, should not scale or clip away under the graver, and not interfere in any way with the work of the artist; the least touch of the graver must reach the wood and make its impression. Lastly, the design should be permanent. These difficulties will be avoided by adhering to the instructions given in the lines following.
The solution to render impervious the surface of the wood consists of
| Common gelatine | 5 parts |
| Gum arabic | 3 parts |
| Castile soap | 3 parts |
| Water | 100 parts |
Dissolve by heat on a water bath.
To apply it, the wood is rubbed with fine sandpaper, then heated over a spirit lamp to about 86 deg. Fahr. (30 deg. C.) and upon it is poured in excess the liquefied and quite warm solution, which must be allowed to penetrate in the pores of the wood by letting it gelatinize, when it is wiped off clean. Nothing must remain on the surface of the wood. This done, and while still damp, the preparation is rendered insoluble by pouring over a solution of alum at 5 [pg 56] per 100 of water. The object of this preliminary operation is to render the wood impervious, and therefore to prevent the sensitizing solution to penetrate its texture. The wood is then heated again and its surface whitened with a little silver white or sulphate of barium, diffused in a small quantity of the following warm solution:
| Gelatine | 1 parts |
| Alum | 0.1 part |
| Water | 100 parts |
While wet, this is smoothed with a jeweler's brush, taking care to leave on the wood, a very thin layer of the mixture, only sufficient to obtain a white surface which, by contrasting with color of the wood assists the engraver in his work. The wood should now be allowed to dry thoroughly, when it is coated with a tepid solution of
| Isinglass | 3 parts |
| Water | 100 parts |
and dried.
Now the sensitizing process differs according as whether the cliché is positive or negative. In the former case the preparation is sensitized with the solution employed in the black process, proceeding afterwards as usual; in the latter, that is, when the cliché is negative, the best process is the cuprotype.[12]
For printing, special frames are employed to permit one to examine the progress of the impression from time to time without the possibility of either the wood block or the cliché moving. These frames open in two. The upper frame is provided with screws on the four sides to hold firmly the block when it is placed into contact with the cliché by means of the screws fixed on the cross bars. As to the cliché, if it is made on a glass plate, it is secured on the thick glass plate of the lower frame by two wooden bars against it pushed by screws.
When the block is ready for printing, the prepared side is usually concave. It is straightened by slightly wetting the back and resting it on one end, prepared side against the wall.
Printing on Canvas.—The canvas should be first brushed with a solution of aqueous ammonia in alcohol, 1:3, to remove greasiness until the thread just commences to show, then, when rinsed and dry, rubbed with fine sand to give a tooth, dusted, washed with a sponge and then coated with the following solution, proceeding afterwards as in the cuprotype process:
| Isinglass | 8 parts |
| Uranic nitrate | 5 parts |
| Copper nitrate | 2 parts |
| Water | 200 parts |
Printing on Opal, Celluloid, etc., is quite simple; it suffices to coat the material with the following gelatine solution, and, when the film is dry, to proceed in operating by any one of the processes before described.
The sensitizing compound may be incorporated to the gelatine solution, but we prefer not to do it and to sensitize the plates as they are wanted for use.
| A. | Gelatine | 4 parts |
| Water | 70 parts in volume |
Dissolve and mix little by little in order:
| B. | Chrome alum | 0.25 parts |
| Water, hot | 20 parts | |
| C. | Alcohol | 10 parts |
When coated place the plates on a level stand until the gelatine is set, and let them dry on a rack.
Transparencies.—Prepare the plate as directed above with
| A. | Gelatine | 6 parts |
| Water | 70 parts | |
| B. | Chrome alum | 0.3 part |
| Water, hot | 20 parts | |
| C. | Alcohol | 10 parts |
Sensitize with the uranic-copper solution employed in the cuprotype. By this process transparencies of a rich brown, [pg 58] not actinic, color are obtained. Consequently they can be used to reproduce negatives by the same process. For lantern slides they may be toned black by platinic chloride.
To strip off the picture, apply, first, on the glass plate a substratum of India rubber, 2 to 100 of benzole, coat with plain collodion, immerse the plate in water as soon as the film is set, and when greasiness has disappeared pour on the gelatine solution and proceed.
For tranferring on any material, a sheet of paper is immersed in a solution of India rubber cement in 20 parts of benzole, dried, coated with the gelatine solution, sensitized, etc., by operating in the ordinary manner. After development, the proof, being dry, is brushed over with alumed gelatine moderately warm, dried, immersed in tepid water until the gelatine is softened and tacky, when it is placed on the material and squeezed into contact. This done, the transfer should be allowed to dry thoroughly. Now, by imbuing the proof with benzole to dissolve the India rubber, the paper is easily stripped off, leaving behind the picture adhering to the material.