Cotton or Cotton/Poly telling the difference
 

I've checked the archives, didn't see an answer to my question. Can someone tell me how to look at a piece of material, (stuff we already have on hand or is given to us) and tell if it 100% cotton, what do I look for?

There are two ways to tell the difference. The number 1 way is to snip off a piece and burn it. If it has poly content it'l spit and leave hard black chunks. The other way is to just squeeze a handful for a little bit. 100% cotton will wrinkly and poly cotton won't.

Burn a tiny piece. Cotton burns to ash while fabric with polyester will blacken and bead. The scrunch test will also work.
Cotton will crease while polycotton creases much less. Iron a piece. Polycotton will smell, change colour a little and begin to shrivel a little with a really hot iron while cotton does not.

This is very helpful -- I get fabric donated to our local chapter of Project Linus all the time, and sometimes I really can't tell on the solids. I have definitely noticed the smell, though, and wondered if that was an indicator. Thanks for letting me know that it is!

Yep, the burn test.