Besides the well-known, every-day tones we see, which never outstep the narrow range between chocolate brown and purple, a practically infinite variety of color, from chalk red to black, may be obtained by a little careful study of toning baths instead of regarding them as mere unalterable machines. Most charming tints are produced with platinum baths, a good formula being
| Strong nitric acid | 5 drops |
| Water | 4 ounces |
| Chloro-platinite of potassium | 1 grain |
The final tone of a print cannot be judged from its appearance in the bath, but some idea of it may be got by holding it up to the light and looking through it. A short immersion gives various reds, while prolonged toning gives soft grays.
Results very similar to platinotype may be obtained with the following combined gold and platinum bath:
| A.— | Sodium acetate | 1 drachm |
|---|---|---|
| Water | 4 ounces | |
| Gold chloride | 1 grain | |
| B.— | Chloro-platinite of potassium | 1 grain |
| Water | 4 ounces |
Mix A and B and neutralize with nitric acid. (The solution will be neutral when it just ceases to turn red litmus paper blue.)
Another toning agent is stannous chloride. Two or three grains of tin foil are dissolved in strong hydrochloric acid with the aid of heat. The whole is then made up to about 4 ounces with water.
Toning Baths For Silver Bromide Paper.
| Distilled water | 1,000 cubic centimeters |
| Hyposulphite of soda | 100 grams |
| Sodium sulphite | 20 grams |
| Sulphuric acid | 4 to 5 grams |
First dissolve the sodium sulphite, then add the sulphuric acid, and finally the hyposulphite, and dissolve.