Diamond cut

Cut determines how a diamond’s facets meet the light. It should not be confused with shape, which is the stone’s outline when viewed from above.

Three expressions of light

• Brightness: white light returned from the diamond.
• Fire: light separated into spectral colours.
• Scintillation: the pattern of light and dark, and the flashes seen as the stone or viewer moves.

A well-balanced cut allows these effects to work together. Greater carat weight cannot compensate for proportions that return less light to the viewer and allow more light to leave the stone through the pavilion.

How cut is graded

GIA’s overall cut scale for standard round brilliant diamonds in the D–Z colour range runs from Excellent to Poor. The assessment covers both appearance and craftsmanship, including proportions, polish and symmetry.

GIA does not issue an overall cut grade for oval, pear, cushion and other fancy shapes. The report may still list measurements, polish and symmetry. Other laboratories may use their own systems, so always note which organisation issued the report.

What you can see for yourself

• View the diamond in more than one type of light.
• Move the stone and notice how light and dark areas change.
• Check that the outline feels balanced and that any points or corners are symmetrical.
• Compare stones of a similar shape and weight side by side.

The report gives the comparison structure. The actual stone reveals which light pattern you prefer.

Continue to diamond shapes, see all four Cs or find a diamond.