How to remove dark “stains” from such materials as Zimbabwe Black?
These are not real stains, but xenoliths, i.e. materials of a different nature and composition that are contained in the stone itself. The “stained” look is generally removed by treating the surface with acid solutions (normally phosphoric acid). Good results can also be obtained by treating the material with suitable polymers that darken the surface of the stone, thus disguising the “stain”.
