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There are basically two types of colour film, negative and slide (often known as reversal or transparency film). Colour negative is by far the most widely used, not least because it exhibits greater tolerance of exposure errors and is therefore appropriate for the mass snapper market. However it is also an extremely capable medium and is used by many professionals. Slide film is used by serious amateur enthusiasts and professional photographers, and is the preferred medium of magazine editors.

Two main types of slide film are available, and each requires a different processing method. Kodachrome must be returned to Kodak because it is more or less the only company able to for process it. However, E-6 films can be processed by most local laboratories or done at home in a darkroom.

The equipment required to process an E-6 slide film is substantially the same as for processing black-and-white stock, although a rotary processor is a useful. This automatically agitates the tank, leaving leave the photographer's hand free. The need to maintain the chemicals at a constant temperature also makes an accurate thermometer essential. Processing temperatures should generally be kept within a tolerance + or - 1 C°. This is most easily achieved by using a water bath, a deep plastic dish to which hot water can be added as required. Alternatively, a small thermostatically-controlled electric heater can be used to maintain water temperature.

A number of easy-to-use processing kits are available. Most are of the three-bath type, and contain a first developer, a colour developer, and a bleaching and fixing agent. Cross-contamination is a potential problem in the domestic environment, so measures and containers must be washed and cleaned thoroughly. The chemicals have a short shelf-life once mixed, so prepare only what is needed for the immediate processing. In broad terms, the purposes of the three processes are as follows:

  • Using the first developer is basically a black-and-white process. If films were fixed after this first stage they would be revealed as monochrome negatives.
  • Colour films are basically a sandwich of different colour-dye emulsion layers through which light passes. It is the job of the colour developer to bind all the colours together in a final image. It also incorporates a reversal process which changes the images on the film from negative to a positive.
  • The bleaching and fixing agent removes unwanted dyes and unexposed silver particles, and reveals the reversed colour image. A film viewed prior to this stage would resemble a roll of brown tape.

Note that colour processing chemicals are toxic. They must be used with great care and disposed of in a responsible manner. Observe the instructions provided with the processing kit.

To process a film:

  • mix the required chemicals and place them in a water-bath to achieve a processing temperature of 38°C (the water bath should be about 40°C;
  • load the film into the developing tank;
  • fill a two-gallon bucket with water at 42°C to be used as a preheat bath and for rinses;
  • make ready some wetting agent to be added to the final rinse, and a few cloths to wipe away spilt water;
  • bring the tank itself to the processing temperature by placing it in the bucket of water for about 5 minutes - alternatively fill it with clean water at 42°C and leave for about one minute;
  • fill the tank with the first developer, agitate immediately for 10 seconds and then at intervals of 30 seconds for 6 ½ minutes;
  • pour the developer back into its container;
  • wash the film with clean hot water for 3 minutes, making sure that the water is changed several times;
  • fill the tank with the colour developer and agitate as above for 6 minutes;
  • pour the developer back into its container;
  • wash the film again for 1 ½ minutes, using several changes of water;
  • fill the tank with bleaching and fixing agent and agitate for 1 minute, then every 30 seconds for 10 minutes;
  • pour the agent back into its container;
  • wash the film for 4 minutes using several changes of water;
  • add a few drops of wetting agent on the final rinse;
  • leave for 1 minute; and
  • finally take remove the film from the tank and carefully hang it up to dry.
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