Temperature and timing control

Processing tank is naturally the most important piece of equipment but various other items are necessary and there are a few others that can be used to make the process easier. A vital addition is a good photographic thermometer. The modern film processing is a time and temperature operation. A given film developed in a given solution has an optimum development time at a given temperature. The preferred developer temperature for black and white films is 20° C (68° F). Few photographic thermometers are in fact completely reliable, not even those certified as such. However, any error they may show is generally small and can be tolerated by black and white films if the processor takes pains, as he should do, to establish his own development times. If his thermometer has a significant error, he will find that the manufacturer’s recommended development time needs to be adjusted to his operating conditions. The spirit thermometers are perfectly suitable and in practice are generally preferable. The main function of the thermometer in black and white film processing is to check the developer temperature before it is poured into the tank. Some tanks allow thermometers to be inserted to monitor the temperature during processing. The photographic timer can provide the same facilities but the operator has to reset the time after each step in the sequence. The digital watches so popular and it is possible to use the elapsed time facility in a similar manner but on most watches that is much more troublesome to set than on a simple clockwork timer.