Bohin chalk marking pencil set
One of the best markers on the market is the Chalk Cartridge Set from Bohin.
An easily changeable pen style cartridge comes with its own sharpener and a set of chalks in pink, blue and white.
Widely used by long arm quilters as the chalk just brushes or washes off, but lasts long enough to stitch.
Will not damage your fabric.
Chalk refill sets also available.