For best results, professional photographers treat processed film with a hypo clearing agent to speed removal of the fixer and allow more effective washing. In addition, overfixing may initiate dissolution of silver in low-density areas of the film and bleach the photograph, reducing overall film density.Īfter being exposed to the fixer solution, film must be washed for a time period of 20 to 30 minutes with agitation and a constant turnover of wash water. Fixer chemicals should only be used for the recommended time, because overprocessing of the film may result with incomplete washing and ultimately stain the negatives due to accumulation of excess fixer not completely removed by washing. A variation of the common fixer chemical is ammonium thiosulfate, which acts more quickly than the sodium analog and is the chief ingredient of quick or rapid fixers commonly used by amateur photographers. When the development process has been finished, the film is bathed in a solution of photographic fixer (sodium thiosulfate), a chemical designed to dissolve the undeveloped silver halide crystals still embedded within the film emulsion. If salts, such as magnesium and calcium chloride, are present in the water ( hard water), the stop bath will remove these also. The primary function of commercial stop bath solutions is to neutralize the developing agent, halting the development process and removing excess developer from the film surface. Next, drain the tank and wash thoroughly with either stop bath or tap water. Pour a sufficient aliquot of premixed developer into the tank and agitate according to the manufacturers directions for the proper time and temperature. After the film has been loaded into the tank, it is ready for processing. The most efficient development tanks include spools used to wind the film so that the emulsion side does not come into contact with the film base. Development tanks that hold all available black & white film formats are commercially available at reasonable prices, and can usually be purchased locally in camera shops or variety discount supermarts. In order to process black & white film, which is conveniently done in the laboratory with minimal darkroom requirements, the film must first be loaded into a suitable processing container in complete darkness. The most versatile developers allow contrast adjustment through mixing and development time and temperature variations. Some developers are designed to produce finer-grain results than others and a few are formulated to provide high-contrast negatives. There are dozens of commercially available black & white film developers, many of which are general purpose, while others are intended to be used under a specific set of exposure and processing conditions for target films. A certain level of action by the developer on unexposed silver halide crystals occurs in all black & white film and is termed fog density, but most commercial developing agents are designed to minimize this effect. The concentration of silver in developed negatives is highest in those areas of the photomicrograph that have received the greatest amount of illumination, and is proportionately less in areas that have not been exposed as thoroughly. The developer interacts with exposed silver halide crystals embedded in the emulsion to convert them into particles of metallic silver, which forms the negative image. The basic function of black & white developers is to process the latent image produced on the film emulsion by exposure to light. The image was recorded on Kodak T-Max 100 film and processed in D-76 developer at the recommended time and temperature.Īlthough it is possible to process black & white negative films with only two chemicals, film developer and fixer, better results are obtained when recommended development procedures are adhered to using auxiliary solutions for a stop bath, clearing agent, and a wetting agent. 58 green filter was utilized to modulate contrast in the cell walls, which are heavily stained with fast green. The stain mixture consists of safranin O (nuclei, chromosomes and cell walls), fast green (cytoplasm and cellulose cell walls), crystal violet (starch), and orange G (acidophilic cytoplasm). The specimen employed in this discussion is a brightfield black & white photomicrograph of a quadruple-stained thin section of a pine tree (Pinus banksiana) leaf needle.
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