Yesterday I went on a dyeing spree; it had been the first time I had dyed wool in 2 months. Between renovations in what serves as my studio, the Jewish holidays, and the beginning of school, I haven't had much time or space to dye anything. (I haven't even done that much knitting, for that matter.)
Whenever I dye wool, I mix up the colors in small amounts in tupperware containers, and use sponge brushes to apply the dyes. Often there will be some extra dye. I keep that extra dye in the tupperwares, with the lids on of course, and save it for the next time I dye wool.
Normally, this works just fine, but in one of my dyes there was a not so pleasant surprise:
(I had a lot of trouble getting my camera to focus; this was the best I could do.)
Yeah, that's mold. Fortunately, only two of my dyes were affected, and I wasn't too thrilled with either of the colors (the other was this grey-blue thing).
So don't expect your dyes to last forever.
And at some point I'll update with things that are prettier than moldy dye.