This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
1212. Very soft and artistic three-color prints maybe made by the gum process, and as it is not a difficult process to work, and further is most economical, it is especially recommended for experiment.
1213. Materials, Etc., Necessary. - A supply of ferric citrate of ammonium, ferricyanide of potassium, and bichromate of potassium. The following ordinary artists' moist water-colors, in tubes: Gamboge, carmine and crimson lake. A bottle of office gum, some gelatin, a good quality cartridge paper - smooth for fine detail and rough for broad effects; two flat camel's-hair brushes - one an inch wide and the other one and a half inches.
Ferric Citrate of Ammonia..................................
For use, mix equal parts of 1 and 2 and filter.
1215. Cut the cartridge paper into convenient sizes, and well coat with the sensitizing solution, by brushing on with a large flat camel's-hair brush. Care should be taken that, as far as possible, all brush marks are eliminated,
Gelatin Coating. Prepare a one per cent. solution of gelatin, and with this coat the surface of the dry blue print and again dry.
Gum Coating. Now, of office gum and 10 per cent. solution of potassium bichromate take equal parts. Into this thoroughly mix a sufficient quantity of gamboge moist water color to make of the consistency of milk, and, in artificial light, paint evenly over the sized blue print, avoiding oaks. When thoroughly dry, bring carefully into register on the yellow negative and print until the image is clearly discerned of a brown color. Then float the print face downward in cold water, and let development proceed automatically. When sufficiently developed, hang up again to dry.
1218. Give the dry print another coat of gelatin size and again dry. Then prepare a red coating solution as follows: 1 part gum, 1 part 10 per cent. potassium bichromate solution, and adding about equal parts of crimson lake and carmine make the mixture about the same consistency as milk.
1219. Coat the green print and expose as before; but as the printing of the final coating cannot be easily judged on examination, a piece of chloride paper should be put under a negative of similar density, and when this is printed to the usual printing depth, the gum print will have had sufficient exposure. Develop as directed for the green print.
PORTRAIT STUDY. Study No. 57 A. F. Bradley.
With occasional stirrings, in two or three days it will have thoroughly dissolved and should be strained free from any insoluble particles. This thick solution will keep well, but it must be broken down a little with water for use.
1222. If it is desirable to use cake colors, put into a small open vessel, such as an egg cup, and just cover the pigment with water. After standing for a few days it is ready for use.
1223. The blue base print may be printed in gum if preferred, using Prussian blue for pigmenting.
1224. Registration is easily accomplished by holding the print and negative up to a bright light and looking through them.