Tone H
Tone H Blue (Iron)
Positive Employed Thin or Medium, according to result desired.
Tone in the following:
| Avoirdupois | Metric | |||
| 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.