I tested black Frixion pens on a project that didn't matter. First I washed the finished project to see if they would wash out. First wash was warm water and no detergent. Some marks remained. Washed again with detergent. Almost all the marks came out. Threw it in the hot drier and all marks were gone. For marking my quilts for handquilting, I still prefer my Fons and Porter mechanical pencil with colored leads, but sometimes they don't show up well enough. Then my marker of choice will be a colored Frixion pen.