Scaif

[1] It was invented in the late 15th century by Lodewyk van Bercken in Antwerp.

On the top surface a film of olive oil and diamond dust is placed.

Hovering just above the surface of the disk is a mechanical arm to hold the diamond.

It can be finely adjusted, to move the diamond into the exact position needed for polishing the facets.

As the facets are polished more diamond dust is produced, replenishing the supply.