| A. | Ferric sulphate | 5 parts |
| Water | 100 parts | |
| B. | Sodium carbonate | 2 parts |
| Water | 100 parts | |
| C. | Gallic acid | 5 parts |
| Water | 100 parts |
Dissolve the gallic acid in warm water. Filter each solution. They keep well.
To tone, the plate is immersed for, say, ten minutes in A, then, after rinsing slightly, it is placed in B for the same period, rinsed again and flowed with C until the desired color is obtained. The tone is a splendid purple black color. If a solution of pyrogallol be substituted to that of gallic acid, the tone is green, and to a green bordering to black when a solution of catechu is used, the catechu exerting at the same time a tanning action on the gelatine. After toning, the plate should be thoroughly washed.
A similar process consists to wet the plate under the tap, then to flow over a mixture by about equal volumes of
| A. | Ferrous sulphate | 5 parts |
| Acetic acid, No. 8 | 5 parts | |
| Water | 100 parts, filter | |
| B. | Gallic acid | 5 parts |
| Water | 100 parts |
When toned, the plate is well washed, then flowed once with the alum solution and again washed. The tone by this process easily turns to an inky blue not very agreeable. The action should be stopped a little before the desired color is obtained.
It sometimes happens that the image in drying intensifies more then necessary. It can be cleared with a solution of oxalic or citric acid.
A brown sepia is obtained by toning first with potassium permanganate, 1 per cent. of water, then, after washing, with a solution of pyrogallol. If gallic acid be used instead of pyrogallol, the tone is black. By this process a great intensity is obtained. A dilute solution of ammonium sulphide can be employed as a clearing agent.
Pyrogallol and silver nitrate give a warm black tone.
Potassium bichromate followed by silver nitrate form a brick-red precipitate of some opacity.[34]