To make the ferrous oxalate solution we pour one part of the iron solution into six parts of the oxalate, and it is advisable to add to each ounce of developer at least half a grain of potassium bromide; 5 minims of a 10% solution, made by dissolving one ounce of the bromide in about 9 ounces of water, and then making up to 10 ounces—all chemical.
In about four minutes or less this ought to fully develop a properly exposed plate. If the development is much shorter the slide is apt to have an unpleasant greenish tone, a result that may also follow the use of an inordinate amount of bromide in the developer. The developing solution may be made in quantity greater than is required for one plate, and may be used several times if a little of the surplus and fresh solution is added when the quantity in use becomes slow in action.
For really fine cold black tones the following formula by Messrs. Elliott & Son will be found admirable:—
| A | ||
| Soda sulphite | 1 | ounce. |
| Water | 8 | ounces. |
| B | ||
| Potassium carbonate | 120 | grains. |
| Ammonium bromide | 24 | " |
| Potassium bromide | 48 | " |
| Water | 8 | ounces. |
The developing solution consists of equal parts of A and B.
If either of the above developers is to be used, the exposure is to be kept down as compared with the exposure to be followed by developers intended for very warm tones.
The two developers which follow next, require about the same exposure as the two already formulated. "Ortol" is a reducing agent quite lately introduced by Mr. Hauff, of Feuerbach in Germany, and Mr. Hauff's agents in this country are Messrs. Fuerst Bros., of London. "Ortol" gives the finest tones of the warm black type that we have as yet come across, it is singularly free from fogging propensity, and the tones do not easily degenerate into the greens so apt to occur after severe over-exposure with other "black" developers. We suggest a simple formula:—
| A | ||
| Water | 20 | ounces. |
| Metabisulphite of potassium | 75 | grains. |
| Ortol | 150 | grains. |
| B | ||
| Water | 20 | ounces. |
| Soda carbonate | 3½ | ounces. |
| Soda sulphite | 2½ | ounces. |
To make the developer, take one part of A, one of B, and one of water, and to each ounce of the mixture add one and a half or two grains of potassium bromide. The development of a properly exposed slide will take two or three minutes, and the result will probably be highly appreciated.
The above is worthy to stand alone as representing developers for warm black tones, but the following works well. (Messrs. Elliott & Son.)