Good old copper, used for generations! Depending on charging grit, it is used for CUTTING, PREPOLISHING, or POLISHING with diamond. For polishing, it is usually used for the harder stones, 7 or above. Other than cast iron, it is the hardest metal commonly in use, furnishing flat facets and crisp meets.
This laminated lap has a full 3 mm thick 100 Electrolytic Tough Pitch copper bonded to our standard 1/4″ Aluminum baseplate, and then diamond-turned on both sides for flatness. There is sufficient metal to allow for many resurfacings over the lifetime of the lap (And user.)