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Article: Facet


Facet arrangements and historic diamond cuts

  • Round brilliant cut is the most famous facet arrangement used for diamonds and colored gemstones.
  • The modern Brilliant Cut was devised by an Italian named Peruzzi in the late 17th century.
  • Marcel Tolkowsky calculated the first angles for an ideal cut diamond in 1919.
  • Early round brilliant cuts or Old European brilliant cuts are considered poorly cut by today's standards.
  • Other historic diamond cuts include the Old Mine Cut and the Rose Cut.

Cutting and faceting process

  • Faceting is an exacting procedure performed on a faceting machine.
  • The ideal product of facet cutting is a gemstone that displays brilliance, dispersion (fire), and scintillation.
  • Transparent to translucent stones are typically faceted.
  • Opaque materials like pleonaste and black diamond can also be faceted.
  • Water is used for cutting, while oil or water is used for polishing.

Facet angles and optical performance

  • The angles of each facet must be carefully adjusted to maximize the optical performance of a gem.
  • The minimum angle for a facet to reflect light back into the gem is called the critical angle.
  • Gemstones with higher refractive indexes make more desirable gemstones.
  • Poorly cut gemstones may exhibit light leakage and windowing.
  • Refractive indices affect the critical angle and internal reflections.

The faceting machine and its components

  • The faceting machine uses a motor-driven plate to hold a flat disk (lap) for cutting or polishing.
  • Diamond abrasives are used for cutting laps, while various materials are used for polishing laps.
  • The machine includes an angle readout, height adjustment, and an index gear for setting the rotational angle.
  • A dop stick holds the stone in place, and a transfer jig is used to flip the stone for cutting and polishing both sides.
  • The mast and quill are parts of the machine that aid in holding and adjusting the stone.

The modern faceting process

  • The dopped stone is ground at precise angles and indexes on cutting laps of progressively finer grit.
  • Accurate repetition of angles is aided by the angle readout and index gear.
  • Polishing involves the use of fine abrasive particles to make minute scratches invisible.
  • A transfer jig is used to cut and polish both sides of the gemstone.
  • The process involves cutting and polishing each facet multiple times.

Facet Data Sources

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