APPENDIX.
1. Photo-zinc Process.—2. Gelatine Process.—3. Half-tone.—4. Intaglio Processes.—5. Drawing Materials.—6. Books for Students.—7. Decorative Pages.—8. List of Photo-engravers.
PHOTO-ZINC PROCESS.
FOR THE REPRODUCTION OF LINE DRAWINGS IN RELIEF, SUITABLE FOR PRINTING AT THE TYPE PRESS.
Description of the Process.—The first stage is to have the drawing photographed to the size required, and to transfer a print of it on to a sensitized zinc plate. This print, or photographic image of the drawing lying upon the zinc plate, is of greasy substance (bichromate of potash and gelatine), and is afterwards inked up with a roller; the plate is then immersed in a bath of nitric acid and ether, which cuts away the parts which were left white upon the paper, and leaves the lines of the drawing in relief. This “biting in,” as it is called, requires considerable experience and attention, according to the nature of the drawing. Thus, the lines are turned into metal in a few hours, and the plate, when mounted on wood to the height of type-letters, is ready to be printed from, if necessary, at the rate of several thousands an hour.
The cost of these blocks averages 6d. the square inch where a number are made at one time, the minimum price being 5/-.
Small book illustrations by this process, by firms who make a specialty of producing single illustrations, are often charged 9d. the square inch, with a minimum of 7/6; but the cost should never be more than this for a single block by the zinc process.