For the production of the sensitiveness, or for the production of the correct reproduction of the colours, two eoside of silver dyes, R. and P., are used. The P. dye gives great sensitiveness, and is especially suitable for portraits, landscapes, etc. In using this a {42} correct reproduction of the red must be abandoned, whilst the R. dye gives an absolutely correct colour rendering but requires about double the exposure. Ten ccm. of the eoside of silver solution are added to 100 ccm. of the emulsion. When coloured the emulsion will only keep for one or two days.
The time of exposure with the R. dye is normally from one-and-a-half to three minutes.
After exposure the plate must be well washed under a tap and then allowed to thoroughly drain, or otherwise developing streaks will show.
Hydrochinone developer is used for developing, consisting of three solutions:—
| (A.) Distilled water | 500 | parts |
| Sodium sulphite | 200 | parts |
| Potassium carbonate (pure) | 200 | parts |
| (B.) Hydrochinone | 25 | parts |
| Alcohol (96%) | 100 | parts |
| (C.) Ammonium bromide | 25 | parts |
| Distilled water | 100 | parts |
This developing liquid is concentrated, and is used as follows:—
| Solution A. | 100 | parts |
| Solution B. | 5 | parts |
| Solution C. | 7 | parts |
To obtain hard negatives solution B is increased from 1 to 5 times. A mixture of 150 parts of the above solution with 1000 parts of distilled water forms the actual developer. By the addition of more concentrated developer or increasing the quantity of water the developer may be suited to the character of the subject. The developer must be freely flowed over the plate, and then the plate fixed with sodium hyposulphite. Intensification is effected with—
| (A.) Pyrogallol | 7 | g. |
| Citric acid | 7 | g. |
| Distilled water | 1500 | ccm. |
and when dissolved