Potassium Bichromate 75 grains 5 grams
Ferric Alum (Ferric
ammonium sulphate) 8 ozs. 85 grs. 250 grams
Oxalic Acid 1 lb. 4 ozs. 600 grams
Potassium Ferricyanide 6½ ozs. 200 grams
Ammonium Alum 2 lbs. 2 ozs. 1000 grams
Hydrochloric Acid 10% 6½ ozs. 200 cc.
Water to 50 gals. 200 liters
The method of compounding this bath is very important. Each of the
solid chemicals should be dissolved separately in a small quantity
of warm water, the solutions allowed to cool, filtered into the tank
strictly in the order given, and the whole diluted to the required
volume. If these instructions are followed, the bath will be a pale
yellow color, perfectly clear, and will remain so for a considerable
period.
_Time of Toning_—Five to ten minutes at 70 degrees F.
_Time of Washing_
Wash for ten to fifteen minutes until the highlights are clear. A
very slight permanent yellow coloration of the clear gelatine will
usually occur, but should be only just perceptible, when it will have
no effect on projection. If the highlights are stained blue, then
either the film was fogged during development or the bath was not
compounded correctly. Washing should not be carried out for too long
a period, especially with water inclined to be alkaline, because the
toned image is soluble in alkali.
_Life of Bath_
If the acid is renewed to the extent of the original amount after
toning each 5000 feet, the bath is capable of toning 15,000 feet per
50 gallons of solution.
If even after revival, the tone remains flat, the bath is exhausted
and should be thrown away.
After continued use, a slight bluish sludge will collect in the
bath, but this is not harmful. Should this form, however, to any
appreciable extent, it is due either to incorrect mixing, the action
of light, or to contact with metallic surfaces.