The bath for rendering the plates sensitive does not differ from that recommended for taking negatives with wet Collodion. The formula for its preparation may not be out of place, however, and may assist those whose knowledge of the matter is not perfect.
| Nitrate of Silver (fused) | 1¼ | ounces. |
| Distilled Water | 1 | pint. |
| Iodide of Cadmium | 3 | grains. |
Dissolve the nitrate of silver in half the water and then add the iodide of cadmium; thoroughly agitate the mixture for five or ten minutes, then add ½ ounce of alcohol, sp. gr. ·840, and fill up with the remaining half of the distilled water; further agitation, and subsequent filtration through two thicknesses of white bibulous paper, will put us in possession of a negative bath. The nitrate of silver being fused, and consequently, pure and neutral, and as it is essential to obtain clean pictures that the bath should be slightly acid in its reaction, we find it necessary to add 5 or 6 minims or drops of pure glacial acetic acid to a bath of 20 ounces, in order that the above condition may obtain.
THE DEVELOPING SOLUTION
Is very simple in its nature, being merely a saturated solution of gallic acid in distilled water, to which has been added a small proportion of alcohol of sp. gr. ·840.
The exact formula is as follows:—
| Distilled Water | 1 | pint. |
| Alcohol sp. gr. ·840 | 1 | ounce. |
| Gallic Acid | ½ | ounce. |
The gallic acid will not be entirely dissolved, but that left at the bottom of the bottle will ensure the solution being saturated; it is better not to filter the developing solution until it is required for use, as it is preferable to allow it to stand over an excess of gallic acid, than for it to be withdrawn after a slight agitation with the crystals; it is a great error to suppose that we obtain a saturated solution of gallic acid by merely agitating the crystals with water for a few moments.
The developing solution prepared as above directed will keep good and in working order for some weeks, but when it becomes of a dark color, it would be safer to reject it and prepare a fresh quantity than to run the risk of a failure from an impure and imperfect developing agent.