MISCELLANEOUS PRINTING PROCESSES 315 
Potassium bichromate 58 g 445 gr. 
Water 1000 ccm 16 oz. 
Soak the gelatine and the candy in the water for 30 minutes, 
dissolve by heat, and add the bichromate, Or (Vogel): 
A. Gum arabic 160 g 1 oz. 
Sugar 400 g 24 02. 
Honey 80 g 4 oz. 
Water 400 ¢ 2Y4 02. 
Alcohol 60 ccm 900 min. 
Use warm water to dissolve the gum, sugar, and honey, and 
then add the alcohol; to this should be added a few drops of 
glycerine in dry weather. 
B. Ammonium bichromate, 10% sol. 
For use mix 1 part A, 2 parts B, and 3 parts water, heat to 
oon ( 122" i), and filter twice. 
Plate glass should be flowed with one of the above solu- 
tions, the excess drained off, the plate dried in a level position 
at 63° C. (145° F.), and exposed while still warm. As the 
powder only adheres to the unexposed parts, a transparency 
must be used and not a negative, if a positive is required. In 
bright sunlight the exposure will be from 1 to 2 minutes, or 
until the image is faintly visible. The plate should then be 
again warmed, until hotter than the room in which the work 
is carried out, and placed on a sheet of white paper. A fine 
powder, such as graphite, sifted on to the surface from a fine 
muslin bag, is gently brushed over the whole surface with a 
very soft brush. As the unexposed parts absorb moisture, 
the powder will adhere, and gently breathing on the film will 
cause it to adhere more quickly. As soon as the image is 
intense enough, the excess powder should be brushed off, the 
plate coated with 2 per cent plain collodion, and, when this is 
set, immersed in a 5 per cent solution of alum until free from 
