I don't usually pre wash most fabric. Intense colors I do. This week it was a good thing I prewashed some black fabric, it was a real bleeder. After I saw how dark the color catchers were I put it in the sink and washed it several more times and it was still bleeding. I didn't have anything in the house to set the dye and it would be 100 miles round trip to go buy some. I put the fabric in a large pan and boiled it, rinsed then took a very small piece of white fabric , put it inside a wad of wet black fabric to see if it was still bleeding. After about a half hour the white was still white and I can use the black fabric. Glad I took the time to pre wash this time.