When I first painted some thread, most of the color washed out. I needed to figure out how to fix that as vibrant color is my thing. I used to dye fabrics and realized that while I either washed the fabrics or used prepared for dye fabrics, I wasn’t doing that with the threads.
Even though paint sits on the surface, I thought the answer might be to wash the threads first. I hank the thread, tie it like you see the yarn tied, so it doesn’t knot up and become a mess. In a bowl I put a little mild soap and gently swish the thread around. I rinse it the same way and pat it to get part of the water out.
I like to paint wet thread as the paint moves more and creates nicer colorations. I hope that helps anyone diving into painting instead of dyeing.