sharon, i do queen quilts on a long-arm frame. i TRY to mark one row across at one time, while it's on the frame. then i stitch that row, roll it, and mark the next row and so on. sometimes, i mark a row and get distracted before i complete that row or series of blocks. so the marking has to last until i can come back, sometimes 2-3 days later. so the kind that disappears won't work. we're talking about wash-off.
but i haven't been able to find a fine-line wash off. i tried the chalk markers, that work like the old scripto lead pencils but they get very blunt in no time and then they lose the real line, especially around curves. i tried one of those white chalk pencils and a silver pencil but i can hardly see them unless i press down. on the frame there's nothing behind the quilt to support pressing with a pencil, so the pencil kind of digs in.
i may be looking for something that doesn't exist. who knows?