The latest in my continuing series of Very Basic Questions. "What Is
Wood?" should be coming along soon.

I put a first coat of finish on my (second pair of) face frames last
night; MinWax Satin Poly, cut about 40% with mineral spirits. I put four
coats of the same on the first two face frames and I like the results.

Up to now I've been cutting off another piece of tee-shirt for each
coat, hanging the used cloth over the edge of a flower pot in the yard
until it's safe to discard. The shirt is almost used up so on a whim I
put the piece I was using in the (3/4 full) can of poly and put the top
on. Any reason I can't use that piece of cloth again tonight? Was this a
bad idea in some other way, like that the can of finish is now ruined?
Should I perhaps have stored the cloth in a ziploc bag instead?