THE IRON PROCESSES 261 
Water 1000 ccm 16 oz. 
Wash with distilled water, and fume with ammonia, expose 
to light, and develop with ferrous oxalate; then wash thor- 
oughly. 
The cyanotype process may be used for making lantern 
slides or transparencies, though, naturally, the colour is suit- 
able for but few subjects. The sensitising solution is rather 
weaker than used for paper: 
A. Ferric ammonium citrate 
(green) 250 g 4 oz. 
Water 1000 ccm 16 oz. 
B. Potassium ferricyanide 100 g 768 gr. 
Water 1000 ccm 16 oz. 
Mix in equal volumes and filter. Gelatinised glass (fixed out 
dry plates may be used) should be immersed for 5 minutes, 
and rapidly dried. The sensitiser will not keep when mixed. 
The plates should be exposed like the paper, and washed in 
the same way. 
PELLET’s oR Gum-IRon Process.—This process gives blue 
lines on a white ground, thus the reverse of the cyanotype 
process, from a drawing or plan. The paper has very poor 
keeping qualities. Originally patented by Pellet. Three 
stock solutions should be prepared (Pizzighelli) : 
A. Gum arabic 200 g 5/5) oz 
Water 1000 ccm 16 oz. 
B. Ammonio-citrate of iron (red) 500g 8 oz. 
Water 1000 ccm 16 oz. 
C. Ferric chloride 500 ¢ 8 oz. 
Water 1000 ccm 16 oz. 
These solutions will keep indefinitely in the dark, with the 
exception of A, which becomes acid in about a week. For 
use mix in the following order: 
_A solution 200 parts 
