Berol China Markers are a lab standard for editing , because they mark on almost any porous or non-porous material without scratching the surface.
They allow you to write on photos without it being permanent.
The wax color rubs off with a soft cloth or tissue. To sharpen simply peel for more marker.
Wax china marker, ideal for smooth glossy surfaces
Easy to sharpen by pulling a fine cord to unwrap a new length of wax core