I just finished a batik quilt for my oldest daughter. I did blue blocks and sand blocks with blue appliques. I never prewash because I think they cut more precise but that's just me. I washed it the day before yesterday with a color catcher and dried it. The color catcher was blue and I sent her two of them but no bleeding issues on the quilt. Hope that helps, your going to get divided advise. The biggest difference I've noticed between cotton and batiks are that batiks have no give. When piecing you have to be alert and there very little room for error lol I'm not perfect so I don't do star projects with batiks.