316 PHOTOGRAPHIC FACTS AND FORMULAS 
yellow stain, then rinsed and dried. Instead of using the 
collodion, the plate may be treated with: 
Sulphuric acid 75 ccm 1 oz. 
Water 300 ccm 4 oz. 
Methy] alcohol 600 ccm 8 oz. 
until all yellow colour disappears, then gently washed with 
water, and dried. The image is very tender and very liable 
to damage. If it is not to be stripped from the glass, it is 
advisable to give the glass a preliminary coating of a 2 per 
cent solution of sodium silicate. 
THE PEPPER DUSTING-ON PROCESS.— 
A. White pepper 400 g 8 oz. 
Benzole 1000 ccm 20 oz. 
Allow to stand for 24 hours with frequent shaking; then 
filter. 
B. Gum dammar 50 g 1 oz. 
Benzole 1000 ccm 20 oz. 
C. Solution of rubber in benzole; bicycle tire cement will do. 
For use mix 10 parts A, 1 part B, 1 part C, filter, coat any 
surface, and dry in the dark. Expose under a transparency 
for a few minutes in the sun, dust over with any dry litho or 
other colour, or bronze. Finally brush clean with a soft 
brush. 
NEGROGRAPHIC Process (Itterheim)—Smooth well-sized 
paper should be rather thickly coated with: 
Gum arabic 250 g 4 oz. 
Water 1000 ccm 16 oz. 
The gum should be in clear small lumps and preferably sus- 
pended in a fine muslin bag in the water, which may be warm. 
When all has dissolved, add: 
Potassium bichromate 50 g 384 er. 
When this has dissolved, add: 
Alcohol 10 ccm 77 min. 
