Originally Posted by MTS

Clover's Tailor's Chalk will make a really thin line. Available at Joann's.

And those Clover Chalk Wheels (mentioned above) are really versatile.

@quilt1950
I never thought of using soap, but that's a great idea. At least you'd sure it would wash out.

But I wonder if it produces a thick, waxy line that would be harder to hand quilt through. I'm going to have to try that next time.

Did you just slice off a piece from a bar to get a sharp edge?