Name: Kait
Message: Why does the dye not keep longer than a week? What happens if you use 'old' dye? Why is it necessary to pre-soak the material and rinse it after? Rinsing after seems to lessen the color. Thank you

Fiber reactive dye ideally reacts directly with the fiber, given the fiber, the right pH, and the right temperature. Unfortunately, it will also react with water. Procion MX dyes are the most reactive of reactive dyes, that is, they react the most quickly, so they go bad after a week or two in solution, at room temperature. (They last much longer if refrigerated, but you must allow the dye to return to room temperature before using it.) Cibacron F dyes are very similar to Procion MX dyes, but they are less reactive and stay good much longer in water. Drimarene K dyes are less reactive still and can actually be purchased in liquid form, and yet they are reactive enough to be used like Procion MX dyes, if you make sure that they are warm enough (preferably above 95 degrees F) while they react with the fiber.

There are other reactive dyes, such as Procion H, which are even less reactive, and thus are commonly purchased already dissolved. They require steaming to fix to the fiber, however.

What happens if you use 'old' dye? It will just wash out of the fabric. Once reactive dye has reacted with water, it cannot react with fabric, and thus is no use at all as a reactive dye. It cannot be fixed to cotton or linen. However, it can still be used as an acid dye, with vinegar, on protein fibers such as wool. For a recipe, see PRO Chemical & Dye's "Direct Application on Wool using PRO MX Reactive Dyes".

Rinsing lessens the color only because the useless unreacted dye is being washed away. Just use a little more dye, and also be sure that you use the right pH (the right amount of soda ash) and proper reaction temperatures (typically 70 degrees F. or high for 24 hours). If your colors are not bright enough after rinsing, then you are doing it wrong. See "Why did my tie-dyes come out too pale?", or "FAQ: My colors are not very bright. What did I do wrong?".

Pre-soaking is just one of several ways in which you can add soda ash to the reaction, allowing the pH to be high enough that the fiber reactive dye can react with the cellulose in the fiber. See "What is soda ash, and what's it for?"