Butterflywing, thanks for this great lesson on cotton fabric!
I don't know what thread count the old sheets are that I have, but I do know that if I follow this procedure:
1. Wash with no fabric softener
2. Hang them out on a sunny day to dry
3. Put them immediately on the bed without folding
They feel and smell just like the beds at home when I was a child. Just a little rough but soft at the same time, and heavy. I can't find any more sheets like them.
Do they still make any sheets in America? I haven't been able to find any.