I have a soapstone marker that I used to use since it is made for just that purpose and it worked ok I guess, but it was constantly needing to be sharpened. As soon as you use it the tip flattens out and I like a nice thin line. On dark fabric I use a fine white marking pen by Clover. The marks iron right out (or steam so the iron doesn't have to touch the fabric). It takes a few seconds for the marks to appear when you first mark with it, but after that the stay until you heat them to remove. I like it the best of anything else I've tried. There's a thread on here today about using chalk though and I'm interested in checking that out because with chalk you can see what you mark right away.