When quite dissolved add B very gradually to A, shaking almost continuously. The fixed print should be washed for at least fifteen minutes before toning and should then be placed in a clean tray while the toning bath is poured over it. The solution must be kept moving and the print must be removed and washed directly the desired tone is reached. Prolonged immersion will cause the print to acquire a deep blue tone.
Brown and Red Tones with Uranium.—Prints immersed in the uranium toning bath gradually become warmer in tone, changing from black to brown and brownish red until they assume a deep red nearly approaching the well-known Bartollozzi chalk.
Prints to be toned by this process must be thoroughly free from hypo or stains will be the inevitable result. The toning bath should be made up as follows, and it must be used at once as it will not keep after mixing A and B:—
| A. | ||
| Potassium ferricyanide | 20 | grains. |
| Water | 20 | ounces. |
| Glacial acetic acid | 1 | ounce. |
When quite dissolved add
| B. | ||
| Uranium nitrate | 20 | grains. |
| Water | 1 | ounce. |
Immerse the print and keep the solution in motion until the desired colour is produced, then wash the print for half an hour in several changes of water acidulated (1 dram in 30 ounces) with acetic acid. Weak, under-developed prints are much improved by this method of toning.
At the end of half an hour, if the whites are at all yellow they may be cleared by immersing the print for a minute or two in the following bath:—
| Ammonium sulphocyanide | 20 | grains. |
| Water | 10 | ounces. |
After immersion, rinse the print for five minutes and dry.