I believe it was a thread from this site concerning Fixion pens that make me test them.
First I marked fabric using a stencil and Fixion pen. Ironed the fabric to remove the pen - worked great.
Put the fabric in the freezer and pen returned. Ironed again - no change. Washed the fabric - no change.
I have made intricate baby quilts with lots of quilting using stencils and Fixion pens. If I didn't care for the stencil I ironed the pen away and started over. I'm sick to think that if any of the quilts I made are stored in a cold attic or taken in a car during an Ohio winter, they will be ruined. I've learned my lesson.
LQS and quilt shows sell the pens and I believed they were the best thing since sliced bread. The manufacturer does not recommend them for fabric marking where it will show and they suggest an ink solvent that may work to remove some of the ink.