There are very few things as valuable as a shop rag. It's used for a variety of purposes, but the whole idea is that when it's done, you throw it away without a second thought. Sure, shop rags can be washed, but eventually they're done. Throw it away .
I make mine from old tee shirts. I can get 10 shop rags from a single shirt. When a tee-shirt has reached the end of it's service life, it goes under the scissors. First I cut off the sleeves, which make two small rags. Then I cut the shirt across the top and sides, which gives me two big pieces of cloth. Cut each of those into quarters, and that's a total of 10. Four quarters, plus the sleeves. One of those rags has a pocket, because I use pocket tee-shirts.
I make heavy-duty shop rags from the legs of old blue-jeans. Sometimes, a piece of good, blue denim is just the ticket for a particular project. Gun-cleaning, refinishing furniture, light mechanic work, there's nothing like a good shop rag, and while blue denim is durable, there's some times when you just want a piece of nice tee-shirt. Just a few minutes ago, I looked down at an old tee-shirt I was wearing and decided that it should never again be seen in polite company. I took out my scissors and converted it into shop rage. Now it's got a new life and a new reason for existence.