The C41 colour negative film processing cycle involves the use of three chemicals, a colour developer, a stop bath and a combined bleaching and fixing agent, which must kept at a constant temperature. This can been done using a water bath about the size of a domestic washing-up bowl. Although the size of the bath is not particularly critical, larger sizes potentially provide a more stable temperature. Hot water can be added at regular intervals, allowing excess cooler water to drain away through an overflow.

Prepare the chemicals in accordance with kit instructions. Containers must be absolutely clean to avoid cross-contamination. The normal processing temperature is 38^oC although it is acceptable to work 2 C^o either side of this provided colour development times are adjusted accordingly. The bleach and fixing time remains unchanged. The whole processing cycle should take about 20 minutes

Colour development and agitation times are critical to maintain satisfactory repeatable results. Rinse times quoted in processing-kit guides are generally minimums, as are the bleaching and fixing times. Longer cycles do not normally produce adverse effects.

To process a film:

• load it into a development tank in complete darkness - even small neon lights cause fogging and colour casts;
• ensure the chemicals are maintained at the chosen processing temperature;
• preheat the tank and film by adding water 2 C^o warmer than the chosen processing temperature, and drain after 1 minute - discoloration of the water is normal;
• fill the tank with colour developer, and lightly tap it on a hard surface to release trapped air bubbles;
• agitate for 20 seconds, then for 5 seconds every 30 seconds throughout the development period;
• pour out the developer and save for possible re-use;
• fill the tank with the stop bath and agitate for 30 seconds, then drain;
• fill the tank with bleaching and fixing agent and agitate for 30 seconds, then for 5 seconds every 30 seconds throughout the fixing period;
• drain and save agent for possible re-use;
• wash in warm water for approximately 5 minutes using numerous changes of water; and
• rinse in warm water with a few added drops of wetting agent, and then hang up to dry in a warm dust-free place - a slightly milky appearance is normal and disappears during drying.