What is the best way to store unused chemicals (powder)?
Hi, as I start my journey of 're-discovery' of traditional printing techniques (salt printing, cyanotype etc) I would like to ask a couple of questions on chemical storage.
1) What is the best way of storing chemicals in powder form? They arrived in plastic bags, so I have stored the bags in a plastic selaed container/box and put them in my fridge - is this OK?
2) Do chemicals have a shelf life? I have some powder form of toners and D76 that have been on my shelf in the darkroom for 18months. Now I have a fridge in the darkroom will they be usable if I store them in the fridge for future use, or should I just bin them?
many thanks in advance,
Packaged dry chemicals should generally be mixed in their entirety, because you can't guarantee that the components are uniformly distributed in the bag. If you can't use a whole bag of D-76 before it expires, and you can't get a smaller bag, then you might consider mixing your own chemistry from bulk chemicals in whatever quantities you need.
To get started, take a look at Steve Anchell's The Darkroom Cookbook--
If you're asking how long packaged chemicals can keep in their original packaging, usually for a very long time--years.
If you're talking about the storage of bulk chemicals, most of them do just fine on the shelf for years. Some are hygroscopic, so they should be kept dry, and some like glycin are sensitive to light, so they need to be stored in the dark. Refrigeration isn't necessary for most dry chemicals.
The most general answer is to keep them cool and dry. There is a fair amount of variation from one chemical to another. Some things, like dry glycin) just seem to deteriorate over time. Others, like sodium carbonate, form hard to dissolve lumps. Some are photosensitive (notably silver and iron compounds, but also others) and need to be protected from long exposures to light. In general, keeping stuff in the dark (more or less) is a good idea. Protecting developing agents and other reducing agents from air also makes sense. Not buying more than you will need in the next year or so makes sense, too.