Asscher-Cut

An asscher is a square step cut with its corners trimmed, and looking into one you see concentric squares dropping away toward the center — the windmill. Because the facets are broad parallel planes rather than tiny brilliant facets, it flashes in slow wide blocks and it hides nothing: anything inside the stone is on view through the open table.

Judge it face-up for clarity and for the evenness of that square-in-square pattern, which is where a lazily cut one falls apart. The cut corners mean it seats safely in a plain head. Standard millimeter sizes.