Bneighbor

I did a test with mine. I wrote on fabric, let it sit for the night them pressed the fabric in the morning. The markings disappear. I put the fabric in the fridge and the marks came back. I tried all three colors ( red, blue, black). All worked well. I repeated the test, but this time I washed it after heat removing the marks. I then put the fabric back in the fridge, and the markings did NOT return. I am very satisfied with the pens, and I feel confident to use them to do SOME marking for quilting and for my machine embroidery. I say "some", since I only tried it on cotton and poly/cotton blend. I would test on whatever fabrics i use in the future, since I sew with all types of fabrics.
As for marking a quilt, I would always test. The marks would be erased by the heat of an iron, but then you must wash the quilt to finish removing the "magic ink" markings. Funny story from one of our quilting friends who said she did not wash the quilt, but sent it to her friend. The quilt was sent by UPS and the truck was very cold. When her friend opened the box, the markings had reappeared! Sitting in the cold truck was enough to trigger the ink!