10 PHOTOGRAPHIC FACTS AND FORMULAS 
ing solutions are required: A. 10 per cent silver nitrate solu- 
tion; B. 25 per cent ammonia solution; C. 10 per cent caustic 
potash solution; D. reducing solution as follows: 
Sugar 90 g 690 gr. 
Nitric acid 4 ccm 30 min. 
Alcohol 175ccm 202z., 380 min. 
Water 1000 ccm 16 oz. 
To make this, dissolve the sugar and acid in the water, boil 
for 15 minutes, cool down, and add the alcohol. The longer 
this solution has been made, the better it works. The actual 
silvering bath is made up as follows: 
A solution 20 ccm 340 min. 
B solution (more or less) 10ccm 170 min. 
C solution 10 ccm 170 min. 
D solution 5 ccm 85 min. 
Distilled water 100ccm 302z., 250 min. 
To prepare the bath for about 700 square inches of glass 
surface, take 1200 ccm (42 oz., 112 min.) of A, and add B 
until the solution nearly clears up, which will take about 
500 ccm (17 oz., 287 min.) ; then add C 600 ccm (21 oz., 
56 min.). The mixture will again become thick; then add 
cautiously more B until the solution clears. It should now be 
a brown colour but transparent. Then add: 
Distilled water 6000 ccm 211 0z., 84 min. 
D solution 300ccm 100z., 268 min. 
The temperature should be from 18° to 21° C. (65° to 
70° F.). With lower temperatures the D solution must be 
slightly increased. Too.low temperatures give too thin films, 
while with too high temperatures the silver film is too soft. 
The glass should be covered with water, and, if the solutions 
are mixed beforehand, the water should be poured off and 
the silvering liquid at once applied; but good results are 
obtained by pouring off the water, pouring on the D solution, 
