288. It is not a good plan to place the plate in water before development, nor to first pour the developer into a dish and then drop the plate into it. Both of these proceedings tend to cause the formation of air bubbles on the surface of the film; these adhere to the film, and, when once formed, are very difficult to get rid of, even when a brush is used. Where these formations occur on the film the developer cannot act, and thus an undeveloped spot is left, which fixes out in the hypo bath, leaving a clear, round spot or hole. Lay the dry plate (film side uppermost) in a dry dish, and then pour the developer over it in one sweep, so as to cover the plate all over with it at once. If a portion of the plate be left uncovered, even for only a few seconds, there will probably be a mark on the finished negative. In order to avoid this danger use plenty of developer. Rock the dish during development, constantly and in both directions. The object of this is two-fold. In the first place, it has a great influence on the vigor and brilliancy of the negative, because the action of the developer releases bromine from the silver bromide of the plate, which bromine immediately combines with the alkali, forming a bromide.

289. Now, bromide acts as a restrainer - i. e., holds back development - and this additional bromide, if not distributed by rocking, remains in the developer at the place where formed, so that the development at that part of the plate is additionally restrained. It will be easily seen that the most bromide will be formed and the greatest restraining action will result just at those places where action ought to be most vigorous. Less bromide will be formed in the less exposed parts. The latter will, therefore, develop more and the former less than they should, producing less contrast - flatness - in the resulting negative. Another result of rocking is to prevent a mottled appearance, which often shows itself when developer is not kept in motion. Do not fix the plate as soon as you see enough detail, but give enough time to acquire density also. It is perhaps the most difficult thing in development to judge when the image is dense enough, and such knowledege can only be acquired by experience with the particular brand of plates employed.

290. No two developing agents are alike in their results. Pyrogallic Acid, Eikonogen, Metol, Pyrocatechin and Hydroquinon, or combination of two or more of these, are the developers generally used. The conditions under which individuals must work are so varied that no one particular formula can be applicable to all. When strong, vigorous printing negatives are desired, pyrogallic acid, in combination with either carbonate of soda or carbonate of potash, is generally preferred; although by dilution and modification as much softness and detail can be produced with this as with any other developing agent. Quick development with strong solutions means a lack of gradation, a forcing up of the high-lights before the developer has time to act on the less exposed parts. Good results can be obtained only by slowly coaxing out the detail, so that all parts of the image come up fairly together.

291. A developer containing too much alkali {carbonate of soda or potash) will cause flat, foggy negatives. All developers should be carefully filtered before use. Considerable care must be exercised if several plates are developed together in a large tray, the edges are liable to strike together, detaching small chips of glass, which adhere to the soft gelatin surface, and thus cause pin-holes. Keep the plates separated by little strips of wood, tightly fitted to the bottom of your tray.