I never prewash myself and have been using batiks for a few years. Of course I tend to buy from the same places unless it is a gift. I have been shying away from blue, red and purples in batiks now. Some of my batiks, if they run together you could not see it because they are wild already. Sorry about the color loss but good idea to use ont he backing. I use retayne and also the Shout color catcher. Am lucky I don't "Catch" many dyes. Hope it all works out. Thanks for the warning.