I use Frixon pens all the time. I have found on some darker fabrics that it will leave a faint almost like a bleach mark when you iron the fabric to make the mark go away especially if you use the red Frixon ink. I don't mark my quilts for quilting with a Frixon for this reason but when I am putting markings on the quilt for sewing and matching patchwork it is my pen of choice because I know that it will wash out where pencil and ink won't. Sometimes I use parchment paper to make a pattern for FMQ where I put it on the quilt as a guide and stitch through the paper. I always use Frixon pens for this because I know if any of it gets on the thread it will wash out. I use a water soluble marking pen to mark for quilting if I am marking directly on the fabric.