Agitation. If a film is placed in a developer and allowed to develop without movement, the chemical action soon slows down because the developing agent in contact with the surface of the emulsion becomes exhausted and bromide (a restrainer) is released as a by-product. When the film is agitated, however, fresh solution is continually brought to the surfaces of the film, and the rate of development remains constant. Therefore, agitation also has an important effect on the degree of development. An even more important effect of agitation is it prevents uneven development. If there is no agitation, the exhausted solution that became saturated with bromide from the emulsion may flow slowly across the film from the dense highlight areas and produce streaks. Constant agitation is usually recommended   for   the   first   30   seconds   of   tank development and for the entire developing time when the film is being processed in a tray. After the initial 30-second agitation cycle, the film should be agitated for 5 seconds, once every minute during the remaining time. The  time,  temperature,  and  amount  of  agitation required   for   a   film/developer   combination   are recommended  by  each  manufacturer  of  film  or developer.   These   recommendations   are   in   the instructions that accompany the film or developer. Another reference source is the Photo-Lab-Index. There are three different methods of processing film by hand. These are as follows: the tray, the sheet-film tank, and the roll-film tank. Each method is discussed here  with  an  example  of  the  darkroom  arrangement used. TRAY  PROCESSING The tray method is used primarily for processing only a few sheets of film. With a lot of experience, you can process as many as 6 to 12 sheets of film in a tray at one time. You will find it easier to work with only a few sheets of film at a time, and repeat the process, than to start all the sheets at the same time and damage them. The tray processing method described here has proven  satisfactory  under  most  conditions  for processing one sheet of film at a time. You should use this method as described and develop the necessary skill using  this  procedure  before  you  attempt  to  use variations. The trays should be considerably larger than the film being processed; for example, 4x5 film should be processed in 8x10 trays, 8x10 film in 11x14 trays, and 11x14 film in 16x20 trays. Ideally, the trays should be arranged in a shallow sink that contains temperature- controlled  circulating  water.  The  trays  should  be arranged with the developer to your left as you face the trays. The stop bath goes next to the developer, followed by the fixer and the wash tray. In  all  Navy  imaging  facilities,  it  is  standard procedure when processing film (or prints) by hand to work from left to right. Rinse the trays with fresh water as a precaution against  contamination,  and  prepare  the  solutions.  When the solutions are ready, place the exposed film holder to be unloaded on a clean, dry area of the workbench near the developer. Set the timer for the correct developing time,  and  place  it  in  a  convenient  location  near  the processing solutions. Then, if you are processing panchromatic film, turn out all the lights. If you are processing  monochromatic  or  orthochromatic  film,  you can  use  a  suitable  safelight. Remove one sheet of film from the holder and submerge it quickly, emulsion-side down, into the developer. Then immediately turn it over (emulsion-side up) and slide it back under the surface of the developer quickly, and agitate it vigorously to eliminate possible air bubbles. The surface of the film must be wetted quickly and evenly; otherwise, developing marks may result. Start the timer just before the film is placed into the  developer. During tray development, the tray should be rocked continuously to provide constant agitation. Be careful that the tray rocking is not too fast and that it is varied at intervals; for example, first front to back, and then side to side to avoid patterns of uneven development caused  by  regular  waves. CAUTION Do not allow your fingernails to touch the film emulsion at any time. Tray  development  involves  constant  agitation,  and development  time  is  usually  about  20  percent  less  than if the same film were being developed with intermittent agitation. When tray agitation is done very slowly, the agitation  should  be  considered  intermittent  and  the developing  time  adjusted  accordingly. When the timer rings, remove the film from the developer, drain it from one corner, and submerge it in the stop bath. Agitate the film in the stop bath for about 5 seconds; then transfer it to the fixer. You must agitate 10-16