I agree that the blue marks may come out with deeper soaking or when you wash the quilt. I loved the precision of the "washable" thin pencil lead - but I had trouble with it not washing out, too. I do love working with the smooth slate rods that can be sharpened in a pencil sharpener. It marks smoothly, stays on better than chalk, and wears or washes out with no trouble: you can put in experimental lines, then change your mind later. You can't mark an entire quilt safely, because with handling it wears off, but the line is fine, and "erasable". I also like it because the slate comes in different colors, from light to dark, and it is wonderfully smooth and cool to the touch. Lovely to use.