Development and Developers
from day to day - Or, at any rate, very different results, unless much more time is allowed when the weather is colder. Pro-bably the most general first estimate as to the correctness of the exposure is based upon the time required for the first details to appear on the plate when in the developer. The slowness with which the developer acts in the winter would much surprise some of those whose work is confined to the summer months ; but even during the summer it is easy to be so misled that not only are fairly well exposed plates cast aside, but one's judgment as to exposure generally is liable to be vitiated or at any rate con-fused. Speaking very generally, it may perhaps be estimated that development takes about twice as long in winter as in summer. A general notion of the chief desiderata to be arrived at in arranging the developing apartment or dark-room will be found under the heading Dark-room, and some kind of plate-lifter to the developing dish is a great convenience ; the simple device of Mr. Charles Simpson, which consists of a strip of tin plate about an inch wide and bent twice, as shown by fig. 42, being one of the most convenient. A general instruction in development is never to expose the plate unnecessarily to light, and to use, at all possible moments, a cover for the dish - a thin sheet of ebonite answering the purpose admirably. No light, it should be remembered, is absolutely non-actinic or without action on the plate. The following general instructions for development, given by Mr. B. J. Edwards, may be taken as summarising the essentials of ordinary practice, not only for ordinary plates, but also for films and isochromatic plates: - When using Isochromatic films or plates great care must be taken to work with a deep ruby light only. Three thicknesses of good ruby glass or two of ruby fabric give a fairly safe working window for ordinary daylight. For lamplight the protection required is of course dependent on the strength of the light employed: two thicknesses of ruby glass or one of ruby fabric will generally be found sufficient, but it must not be supposed that the light in either case is sufficiently non-actinic to have no action. Care should be taken not to expose the film or plate more than is necessary even to this light, especially before and during the first part of the development. It is a good plan to cover over the developing dish or otherwise shield it from the light.