Storage of chemicals

Stock and working-solutions are best stored in capped bottles.
Screw caps work great provided they are free of rust or other foreign materials, have liners or seals, and are tightly screwed down.
However, improperly sealed screw caps are likely a major cause of developer oxidation.

To avoid contamination, no cork, stopper, or cap should be used for more than one type of solution. Glass stoppers tend to stick, especially with alkaline solutions.

Air is one of the worst enemies of a photographic solution. Oxidation can occur even in a tightly capped bottle when the solution level of the developer is low. The air space inside a bottle containing a stock solution increases each time some of the solution is used. This increases the chances of oxidation of the solutions from the air. Therefore, it is best to store stock solutions in small bottles. A small air space should be left so that the volume of solution, which varies with temperature, does not loosen the stopper or cause the bottle to burst. The entire contents of a small bottle of stock solution can then be used at one time.

Temperature during storage is important: developers in particular oxidize rapidly at elevated temperatures, leading to a loss of activity and an increased tendency to discoloration. Storage at too low a temperature may also be undesirable. Some concentrated solutions crystallize readily at low temperatures (such as below 13° C), and are very difficult or impossible to redissolve even when warmed. Repeated temperature changes can shorten the life of many photographic solutions.