One of the advantages of powdered chemicals is a long shelf-life. But once you mix it the clock starts ticking. I was wondering if it's possible to buy a larger batch of powdered chemicals and just mix as needed, being very careful to weigh the amount of powder and use the proper amount of water to keep the ratios correct.
Some problems that I might foresee with this are:
- A single-powder mix might actually consist of different constituents which aren't uniformly distributed in the bag. Could be the case for B+W developer.
- The correct ratio of water to powder isn't a linear relationship.
- A multi-powder mix might need different ratios of the powder if it isn't used in full (non-linear relationship between the parts). For example C-41 kits which usually have 3 parts for the developer.
- My assumption about shelf life is wrong and the powder oxidizes over a limited time frame (say several years).
Is any of this actually the case? Is any specific chemical in the process more prone to it (developer, fixer, bleach)? Or is it a non-issue?