16-mm sound motion pictures, a manual for the professional and the amateur (1949-55)

370 XII. PROCESSING AND RELEASE PRINTING (3) The developing tank* — where the film is developed and the exposed emulsion ' ' develops up, ' ' becoming dark in the process. The usual developer tank is one in which the film is completely submerged in the developer bath. Since development is more uniform and development rate (development gamma) is rapid with a high degree of agitation ("stirring"), various arrangements are used to increase developer agitation. Some of these arrangements include the circulation of developer in thin streams in the bath by introducing the developer at the bottom of the tank and removing developer at the top. Another arrangement introduces air jets at the bottom of the tank to increase agitation. In all cases the film passes alternately downward and upward in a developing tank; directional development effects (such as streaking caused by unidirectional flow of the developer past floAv-disturbance-producing parts of the film, such as sprocket holes) are reduced. Since the by-products of development tend to retard development and reduce development gamma, and since it is the very thin film of developer immediately adjacent to the surface of the film that effects development, it seemed reasonable to believe that a spray jet arrangement might be worked out that would require less developer solution, and yet develop the film in a manner more nearly approaching the theoretical optimum. Such an arrangement is in commercial use at DeLuxe Laboratories in New York where it was designed and built by E. Bertram. This machine is very economical of space ; it provides a high rate of development without any measurable directional development effect and with a very high degree of uniformity. As the spray jet concept seemed fundamental from the viewpoint of theoretical hydraulics, the Bertram machine utilizes spray jets throughout rather than liquid immersion. Unfortunately, no description of the machine or of its operation has been published despite the fact that the machine has been in commercial use for several years. (4) The wash tank — where traces of the developing solution remaining on the film are washed away with water prior to the entry of the film into the hypo tank. Oftentimes there is an air squeegee for removing excess developer solution from the surface of the film before it enters the wash tank. A squeegee is a means of removing excess water or liquid ; it usually consists of two blasts of air, one on each side of the film, to blow off the excess liquid. The film is usually completely submerged in water during its passage through the wash tank; it emerges between tanks. (5) The hypo and the hardener tank — where unexposed emulsion is "cleared" from the film and where formaldehyde or other emulsion-hardening chemicals may be added to the hypo bath if desired. (6) Another wash tank — to remove traces of the fix bath. (7) Tho first stage drybox — where the film, after passing a squeegee, is slowly and partially dried by a steady blast of warm dry air which is usually fed into the bottom of the first-stage drybox and exhausted from the top. The squeegee is especially important at this point, since the film would be badly water-streaked if the water were * Eastman Kodak and Dupont have been evolving film emulsions suitable for hightemperature processing. Recent types of emulsion can be developed as a negative in less than half a minute; the development time for a comparable commercial emulsion would bo about 15 minutes. It is well known that the chemical activity of substances increases rapidly with increase in temperature, and it is indeed a portent of things to come in the near future to find that the development time has been reduced to such a great degree and yet development fog and graininess have been retarded so materially.