text: First of all, ash isn't pure carbon.  It contains particulates of unburnt material, etc.  Secondly, it doesn't matter what the cleaning agent is made out of that counts.  Just because diamond is carbon, doesn't mean you have to clean it with carbon.  What you need to find out is whether or not a particular agent will dissolve whatever you have on the stone, plus not dissolve the stone itself.  Acetone, alcohol, or most other solvents will do this just fine.\n\nHope this helps.