I was asked about the bleach test...
I like to buy yarn at thrift shops but sometimes it isn't labelled. Cotton is easy to identify, I know that when I see/touch it. If the mystery yarn isn't cotton then it's usually obvious if it's wool or acrylic but every so often I can't be absolutely sure. I also like to try to break the yarn with my hands but wool doesn't always break and acrylic doesn't always not break (the weight of the yarn can foil the break test).
If I'm still not sure I drop an inch of the mystery yarn into a jar and cover it with a small amount of regular household bleach. I then put a lid on the jar and place it in a cupboard over the stove. I check on it an hour or so later, or the next morning. Wool dissolves in bleach, acrylic doesn't. I imagine if it's a blend then the animal fiber would dissolve and the acrylic content would remain in the jar.
What about fibers that aren't wool or acrylic? I haven't done tests but I'm guessing any yarn that's made from 100% animal fiber would dissolve in bleach. As for plant fibers, I don't know how long it'd take a worsted cotton to dissolve in bleach but that hasn't been an issue because cotton is the easiest yarn for me to identify, it's just so obviously cotton there's no testing required. Ramie? Silk? Bamboo? Hemp? *throws hands in air* I'll do an elementary school science project on bleach and yarn in my next life, promise. Complete with charts and graphs! See, there'd be a column for time elapsed and ... *snaps back to reality*
I have no good reason for why I prefer using bleach instead of fire to determine Acrylic or Not Acrylic. I think the burn test info about smells puts me off, my sense of smell is unreliable.
I'll get back into mitten production soon, I just needed a week off to concentrate on Other Things.
Almost forgot, last week I did manage to knit up a mindless swatch using the dyed yarns to test for bleeding. I didn't put vinegar in the water and I still couldn't detect even a hint of bleeding into the light blue yarn after a good long soak so it should be fine for the mittens. (Just to be sure I waited for the swatch to dry and unravelled it.)