just a word of caution
Anna,
I like using the Frixion pens too. I would advise a bit of caution though. Several years ago I used one (a black one I think) to make tiny numbers on the front side of some pieces for a table runner to keep them straight. After ironing, I could still see a little "ghost" mark from the pen. It seemed to be some sort of waxy type residue. I couldn't get the marks off and neither could a dry cleaner. Probably no one else would notice them, but I do. So now I make sure I only mark on the wrong side of the fabric when I use them.
And maybe since that happened the ink formulation has changed and that won't happen...