If you want to do this optically just shoot a flashlight across the surface of the stone, hills and valleys of even less than 1mm in height or depth will create

If you want to do this optically just shoot a flashlight across the surface of the stone, hills and valleys of even less than 1mm in height or depth will create shadows revealing most of the otherwise hidden text. But hey, I bet we can get a startup to do this with a only a few million in round A seed money.