Watching a video online I noticed quilts being marked with a specific pen. Researched it, bought it, and now I am sold on the Sewline mechanical pencil. The leads are .9 and since I didn't have a pencil that size I did purchase the Sewline pencil. Easy to grip and has some weight to it for control. The leads are ceramic and do not smear or come off until I erase it or use a dry or damp washcloth and swipe over it a couple of times. The leads come in white, pink, green, yellow and black-which actually writes in a gray. Doesn't take much erasing to get the lines off. Tested all colors on a piece of muslin, and they washed right out. They say to use the special eraser the pen comes with, but I used a Papermate white pearl eraser and the lines came off very easily. I especially like the fact that if I make a mistake in marking anything, I can immediately fix it. Link to demos:
http://www.sewline-product.com/Sewline_Fabric_Pencil