Development and Developers
nearly as possible correct exposure be given ; under-exposed plates when developed appear hard with black shadows, and want of detail in the half tones, while very much over-exposed pictures are usually thin and flat, without sufficient contrast. The colour obtained is also dependent on the length of exposure. The best indications of the correct timing, or otherwise, of the exposure are the time taken before the image begins to appear, and the time necessary to attain the required density. For lantern slides, at least some portion of the highest lights in the picture should be represented by absolutely clear glass, without a trace of fog or deposit of any kind, which would detract from the brilliancy of the image. These plates cannot be satisfactorily developed with any of the usual formulae for negative work, but either of the following formulae will give results perfect in every way. To develop, place the exposed plate in the developing tray, and pour over the developer without previously wetting the film: all danger of air bubbles may be avoided by passing a brush over the surface of the plate immediately after pouring on the developer.
Pyro and Ammonia Developer for Warm Tones.
First dissolve the sulphite and citric acid, and then add the pyrogallic.
For use mix one part of No. I and three parts of No. 2, and dilute with water to double the quantity. The mixed developer may be used over again for several plates. For lantern slides and transparencies from very thin negatives dilute the stock solution with less water. For contact printing under the conditions given above, the exposure for negatives of medium printing densities will be from 20 to 60 seconds. If the correct