OUTMODED PROCESS - GUM BICHROMATE/ALBUMIN BICHROMATE
Chromates are salts of chromium that have an unusual property. When mixed with proteins they will remain in solution until exposed to light. After exposure to light (ultra-violet) they will cause the protein in which they are exposed to congeal - to harden. In effect, proteins containing bi-chromates are fried by exposure to light. They are no longer soluble in water.
a. A stone or plate is coated with gum containing chromate. This
is allowed to dry.
Explanation: The non-exposed areas will wash away.
DIAZO PRINTING PROCESS1 A plate (or stone) is coated with diazo emulsion under yellow or red safe light. The best plates for this have a thin silica coating.
2. Once dry the printing surface is sandwiched with a negative and exposed to light
3. The exposed plate is removed to a well-ventilated sink for development.
Minimal light should strike the plate until developed.
5. With a damp (squeezed nearly dry) sponge the developer is pushed over the entire plate. This creates both the printing and the non-printing surfaces so all of the plate should be contacted.
6. As the lacquer thinner dries from the developer the image will become stronger. After a minute of agitation the image should be quite clear.
7. Once the image is visible the developing sponge may be rinsed and
a small pool of water introduced to the mixture. Continued agitation
should strengthen the image areas as residue from non - printing areas
collects on the image.
9. Rinse the plate and fan dry.
10. Apply Asphaltum Gum Etch (A.G.E.) (commonly called "age") with a separate damp sponge.
11. Roll up and print.
photo lithographic procedures