NOTE: Frixon pens do work great...however if you stick your quilt in the freezer the marks come back as clear as ever. My concern is that if you make a quilt as a gift at the xmas party...the recipeint leaves it in their car overnight, it gets cold. Marks will be there, might cause trouble if they don't ask how to re-remove the marks.
I did do this as a test in my freezer when I inadverntently ironed out my marks (duh)