I use a #2 mechanical pencil almost exclusively. I've never had an issue with the marks not washing out. I use warm water; regular detergent; perm. press cycle; toss in the dryer till completely dry. There are some color fabrics that the lines don't show up on. As others have said, when to mark depends on the type of design you are using. I generally mark after sandwiching but I use a lap desk under the quilt when I do.