I love my Frixion pens. I use them all the time. I have noticed that the marked line sometimes doesn't show right away. It acts like the ink has to dry before it shows on some fabrics. Yes - I know that if someone freezes one of my quilts the marks will reappear, and I know that the chemicals "might" someday cause damage to them, but that does not stop me from using them. I really do love them.
Julie