proportional to the temperature. When the temperature is too low, evaporation is slowed down. When it is too high, the emulsion may be damaged. Roller transport processors provide very consistent processing results and can be converted easily to a new process.  The  disadvantages  of  roller  transport processors are: they can leave scratches and scuffs from dirty rollers touching the film, they require a high amount of maintenance due to the large number of moving parts, and oxidation can be a problem due to the churning  action  of  the  rollers  in  the  chemistry. QUALITY PROCESSING The  processing  required  to  produce  a  quality product of any particular film varies with different developer  and  film  combinations,  time  and  temperature of the process, agitation, the film exposure, and the skill of the darkroom worker. A good, high-quality image is one that is free from all processing faults, including scratches and dirt, and so forth. When processing black-and-white film, your goal is to produce a “normal” negative that is as fault-free as possible. Normal is a rather vague term; however, a normal negative is one that yields a pleasing print or reproduction  of  the  original  scene  when  printed  without a printing filter or with a No. 2 printing filter. When film is exposed and processed properly, it is a normal negative. However, when a negative varies from normal, you should be able to determine what conditions  caused  the  deviation. A negative has several basic characteristics to consider   when   evaluating   quality.   These   basic characteristics are as follows: General negative density or opacity to light. Image highlights or areas of greatest density. The shadows or areas of least density. Contrast or the differences between highlight and shadow  densities. Tonal gradation or the range of grays between the highlights  and  the  shadows. Graininess or the appearance of silver grains in a negative that have clumped together. The size of the clumps determines the degree of graininess in the processed   material. All  the  basic  characteristics  of  a  negative  are affected to some extent by a combination of exposure and development. By studying these characteristics, you can usually determine the cause of an error or poor quality in a negative. DENSITY Density determines how much of the incident light falling upon a negative passes through the image. When a small amount of silver is present in the negative, the image appears thin (transparent), and it has low density. When there is a large amount of silver present, only a small amount of light passes through the image, and the negative is said to have high density. A low density, thin negative can be caused by underexposure   or   underdevelopment   or   by   a combination of the two. A heavy or dense negative is the result of either overexposure or overdevelopment or a combination  of  the  two. HIGHLIGHTS The highlights, or dark areas, of a negative for most purposes should not lack detail. When detail is lacking because the highlights are too dark, the highlights are too  dense  or  blocked  up.  Excessive  highlight  density  is caused by overexposure and/or overdevelopment. When both the highlights and the shadow areas are too thin   and   lack   detail,   the   negative   is   probably underexposed.  Thin  highlights  are  caused  by underexposure   and/or   underdevelopment. This may seem like a repetition of the previous discussion on density. However, a negative could and may have overall good density except in the highlight areas. This situation is a result of exposure latitude that is not great enough for the scene brightness range. SHADOWS The  shadows,  or  the  more  clear  areas  of  the negative, also should contain image detail. If these areas are so thin and weak that they are transparent or nearly so, the shadow areas are said to be lacking in detail. Loss of  shadow  detail  is  caused  normally  by  underexposure. The need for detail in both the highlights and the shadows for photographs of most subjects cannot be stressed too strongly. One is as important as the other in the  production  of  good  photographs. CONTRAST Contrast is the difference in density between the highlights and the shadows in a negative. When this 10-31