How (or if) I mark a quilt for quilting depends on the design of the quilt and the quilting.. some I don't mark at all if I plan on following a design in the fabric or a geometric that follows pattern lines. I have used regular #2 pencils.. but with a VERY fine point. that way the thread covers the lines. I've never had a problem being able to see the lines. I've also used silver or white pencils.