Frixion Ink is PERMANENT
Yes, it becomes "transparent" when ironed but nevertheless, the ink is still "there" and NOTHING AND I DO MEAN NOTHING will remove it. On the label I placed on a king size DWR marked with the Frixion pen, I clearly stated that if / when the marks return to remove them with a hot iron. Any exposure to freezing cold will cause the marks to re-appear. The pen does make very clear lines but just "be warned."
If you don't do any pressing on the marks during the construction of your quilt, stain removers will remove most of the markings. Unfortunately, we have to "press" as we go and this causes the Frixion ink to become PERMANENT.
Again, "Be warned."