I did this once and ironed it and it set it in. Now I buy those blue quilting markers that wash off lightly with a moist rag. There is also a purple one that disappears after a few hours. I used a purple one thinking it had to be washed off and traced a whole quilt top. In teh morning when I got up, boy was I shocked and a little tiffed. It was gone. I thought I dreamed the whole thing. Then I read the directions. OOps.