I would like to reference an article from a quilter (Jenny Lyon) who researched this question about using Frixion Pens to mark ours valuable quilts. I have avoided using them because I had heard of issues that have come up when quilters use them. As convenient as they are, I just didn't want to risk it. I like what Jenny did, because she went right to the manufacturer with her questions. You can go to this page to read her entire entry, or read an excerpt from her article below.
So in summary, straight from the manufacturer’s mouth so to speak, a summary of using the Frixion pens on fabric:
1. Frixion pens combine gel ink and thermo ink. You are marking your quilt with a gel pen that disappears.
2. The marks will reappear if the quilt gets cold (anything below freezing I think-I did not confirm the specific temperature) unless the mark is completely removed with an ink remover. Even after a thorough steam of the marks, they will reappear in the cold. This is part of the inherent chemistry of the ink combination.
3. To completely remove the ink so that it will not ghost or reappear in the cold, you will need an ink remover and also may possibly need to scrub the area. The manufacturer has tested Amodex and Mötsenböcker’s Lift-Off 3 and found them to be fairly effective in removing the ink.
4. Frixion pens sometimes leave a ghost mark after steaming. This is the thermo ink showing on the quilt, not the gel. The Pilot rep said to rid the piece of ghost marks you would need to treat it with the ink removers listed above.
So this is a definitive summary of the Frixion pens straight from the pen’s manufacturer.
For me, I will not use these pens very often because I frequently do competition pieces. I cannot risk having any problems with the marking method I use. I think they are great pens for other marking needs but we need to be aware of their limitations. And remember that the Pilot pen company did not design these pens for fabric.
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In reading other posts, I have seen comments that even these removers didn't help their precious quilts. Nope, not worth it.