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