I use a #2 mechanical pencil whenever possible and never have an issue. I wash the completed quilt in detergent in my machine and toss it in the dryer. Granted some fabrics you just can't see the pencil and then I have to resort to other colors. In those cases I use chalk pencils. I quilt on those marked lines and have not had an issue with those marks coming out either, despite the thread 'picking up' the chalk. Unfortunately since I've never had an issue I can't help you with getting out the marks but if you do a search here there have been several threads on this issue recently.