I bought two markers to write on baked clay. Both turned out to be a knockout. They may not be suitable for this specific surface, even though it says that it works on almost all types of surfaces; maybe I just happened to get slightly defective ones.. I don't know. For the use I wanted them for, they didn't work, which is why I gave them both two stars. On paper, tape, boxes, etc., they might be good, so I'm not discouraging anyone from trying them.