I use them all the time for marking my hand quilting designs. And she is right, no not iron. Mine will go on purple and disappear in a few hours. I learned the hard way, I did half a quilt, and when I went back to it, all the designs were gone. LOL. I also use the blue ink. After you are done, you spritz it with water and it disappears. This way, at least the blue one stays on until you finish. Ironing sets the color. It's safe to iron once the color is gone.