I love these pens and use them a lot. I have heard that if they are not washed out some people have had bleach like lines where the ink was left in over time. I have not had that but have also not left them in over a long period of time. To be safe I wash them out rather than erase them with heat. Back to school sales is a good time to stock up. They are always on my Christmas list as well. Quilt shops sell them and generally in more colors but they are more expensive there than at office supply stores where the color supply is limited.