I've marked before sandwhihing; after sandwhihing; completely and as I go. I've decided that I prefer as I go so the marks don't disappear. Working on a frame you might not have much of an issue with that as there is less handling? I use a hoop in my lap so I suspect that has more friction over the entire quilt thus erasing most markings. I use a plain old mechanical pencil with #2 lead and have never had an issue with it not washing out.