butterflywing, thanks for your great response!
I'm wondering how you learned all this and where I can learn more.
I have to disagree about 200-250 thread counts not being widely available until 15 years ago. That would make it 1994. I've been buying 200 thread counts since my college days back in the late '70s and early '80s. Somewhere along the way, 260 counts came in.
I never bought 120 thread count sheets. I did have some 180 counts, and they were good quality back in the day. I always got them from better department stores, then from Linens 'n' Things when that opened. Then about 10 years ago, I tried a Kmart sheet set by Martha Stewart. It was 180 and it was awful - coarse texture, what you'd expect from Kmart but not what I'd expect from Martha Stewart. Prints had almost disappeared by then, and percale weaves were hard to find.
I just don't like 300+ thread count sheets at all.
Sorry for the digression, but I'd really like to find more info on cottons, printing out your own fabrics (maybe that is from another thread?) and now that you mentioned it, more about the old dyes. I hadn't known they had anything harmful in them.