i also love the sewline ceramic pencils (Fon's & Porter has one out too-the leads are interchangable)
they have a variety of lead colors-make a nice fine line that shows up & you can erase it (with attached eraser-or a separate fabric eraser) or they wash out- but the line is fine enough that the threads cover it. this has become my favorite marking tool-for embroidery, marking quilting lines and applique. they are smooth, easy to use & for me have always washed out- removed without incident.