Tone A
Tone A Red (Copper)
Positive Employed—Normal
After immersion of the well washed film in water for one minute, bathe in the following:
| Avoirdupois | Metric | ||
| Copper sulphate | 1 lb. 11 ozs. | 800 | grams |
| Ammonium citrate (neutral) | 5 lbs. 3 ozs. | 2500 | ” |
| Potassium ferricyanide | 1 lb. 11 ozs. | 800 | ” |
| Ammonium carbonate | 13 ozs. | 400 | ” |
| Water to | 50 gals. | 200 | liters |
Dissolve each ingredient separately in as little water as possible, mix the filtered solutions so obtained in the order given, and dilute to the required volume. The solution obtained should be light green in color and perfectly clear. The ammonium carbonate should be almost transparent and free from white powder, and should be dissolved in cold water, while the ammonium citrate employed should be neutral. Most samples contain acid, which acid would neutralize the ammonium carbonate and affect the resulting tone. The free acid is usually citric acid, and should be neutralized with a solution of ammonia using litmus as indicator.
Temperature of Toning—To obtain the best results the temperature of the bath should be from 65 degrees to 70 degrees F.
Time of Toning—Five to ten minutes.
Time of Washing—10 minutes.
Life of Bath—With use the bath precipitates a brown sludge of copper ferrocyanide, and in consequence becomes weaker by virtue of the loss of copper, though 50 gallons of the solution will tone about 10,000 feet of film.
It is necessary to keep the film entirely submerged in the tank, or constantly in motion when on the drum, otherwise if the film is frequently examined, especially during the first few minutes of toning, streaks are liable to occur.