Shelf life for powders?

Procion MX dye powders will usually last for about two years, if you store the jars tightly closed in a place that does not get much above normal room temperature.

I've had some Procion MX dyes last six years or longer, but others have died after less than two years. If you have some old dyes, do a small test to make sure they can still react with cotton. You might just have to use twice as much, when they get old, depending on how much activity is left. Storage in a hot place can make the dyes go bad in no time. If you leave them in a hot car on a sunny day with the windows rolled up, they may be dead by the next day.

Other fiber reactive dyes, such as Remazol, Drimarene K, Levafix E, and Cibacron F, will last longer before they go bad, assuming proper storage conditions.

Old fiber reactive dyes that have completely hydrolyzed, so that they can no longer react with cotton, can still be used as acid dyes on silk or wool, when an acid such as vinegar is substituted for the soda ash, if some heat is added, such as by steaming.

If you decide to refrigerate your dyes, they have to be sealed in such a way that condensation cannot get in—preferable by placing the sealed jars inside another sealed jar with some dehumifiying crystals in the larger jar. That's how we stored all of our powdered chemicals that were prone to go bad, in my lab in grad school: we put them in the freezer. You have to let the outer jar come to room temperature before you open it, to prevent condensation. Moisture is a major enemy, when you're storing fiber reactive dyes.

Paula