How diamonds are cut

A diamond can only be polished with other diamonds, and the usual round gem has 57 facets.

stations: 6
things upstream: 1
raw source: 1
step from the ground: 1

The short version

Software maps a rough diamond so cutters can plan the best stones. It is split by cleaving, saw or laser, then two diamonds spin in opposite directions and grind each other round. On a spinning wheel, blockers add the 18 main facets and brillianteers add the rest, for 57 in all. The finished gem is inspected and sent for grading.

Scan and plan

A cutter studies the rough, today with software that builds a 3D model and shows the best ways to divide it. Sometimes several gems come from one crystal.

Goes in
Rough diamond
Cleave, saw or laser

The stone is split along its natural grain or sawn with a blade coated in diamond dust. Lasers handle awkward shapes without touching it.
Brute the girdle

Two diamonds sit on spinning axles turning in opposite directions and grind against each other, giving each a rough round outline. This stage is also called girdling.
Block the main facets

Held on a rotating arm against a spinning wheel, the stone receives 8 pavilion mains, 8 crowns, 1 culet and 1 table, which form a template for the rest.
Brillianteer the rest

A specialist adds the remaining facets for a total of 57, polishing on wheels charged with diamond powder. The stone's fire is set here.
Inspect and grade

The polished gem is checked for finish and proportion, then goes to a lab such as GIA for a grading report.

End of the lineCut diamond

Worth repeating

Diamond can only be polished by means of other diamonds.
Cutting and polishing a rough diamond costs about 50% of its weight, even with modern techniques.
India has in recent years held around 90% of the world market in polished diamonds.