I was reading about these pens on a blog....do not remember which one...sorry
This quilter marked the fabric with the black marker, ironed the fabric and the marking disappeared, then she put it in the freezer and the marking reappeared. She washed, iron and froze it once again and the mark came back but not as dark. I would like to beleive that this marker is the anwser to our marking whoas but I am not ready to jump on the wagon.