I’ve always used cerium on leather to polish obsidian, but it’s
It is all in technique; the polish only happens for me during the
brief time as the leather dries out.
Moisten the leather a little and apply a thin slurry of polish, work
the stone pressing fairly hard, as the leather starts to dry it will
drag on the stone harder, it is during this increased dragging that
the polishing occurs.
Stop polishing before the leather gets too dry, the heat can easily
crack your stone, also as you have found, the dry cerium can scratch
Re-moisten the leather and start again. You may have to repeat the
process many times but check your work as you go, you will probably
find polished spots and dull spots showing you where you need to
It’s tedious but worth the effort.
Have fun and good luck!