Toronto. Yesterday I mentioned some darkroom stuff being auctioned this November. One of the items is a dark plastic tube with odd end caps.
In the 1970s, colour chemistry was both expensive and short lived. The amateur photographer of the day used various means to reduce usage, maintain temperature, and prolong chemistry life. A drum with removable end caps allowed processing each sheet in a minimum amount of chemistry.
A tiny (and illegal) coffee cup immersion heater could raise the colour developer temperature higher. The hot liquid was carefully poured into the drum via a light trap. The drum was gently rolled on a flat surface to ensure the enclosed paper sheet was evenly coated and developed. One fly in the ointment was Kodak paper. At higher temperatures this brand of colour paper would go lightly pink. Changing to Agfa paper resolved the issue.
The idea was to raise the chemistry temperature above the desired temperature so by the time it cooled the paper was developed at on average the correct temperature. This worked because development followed a time-temperature curve – longer time at a cooler temperature and a shorter time at a higher temperature.
A more costly commercial system used laminar flow to gently wash the paper sheets with minimum amounts of chemistry and wash water baths. I saw this demonstrated at one of the many photographic wholesale firms in Montreal.