I tried this on a quilt I was making. I threw together a bunch of 8" squares and wanted to sew an X in each square. It's a scrappy quilt and not having alot of time to quilt it took me about a month to get it finished. I had to use light to dark markers depending on the color of the fabric. The top went together quick but it was the sandwiching that took me so long. The marks were on the quilt for about a month. I washed in cold water and all the marks are out. Maybe it does depend on the fabric.
Kris