Beyond the Dome
While cabochons celebrate a stone's interior patterns, Faceting is all about light. It is the practice of cutting flat geometric surfaces (facets) onto a transparent gemstone to maximize its brilliance, scintillation, and fire.
The Anatomy of a Faceted Gem
- Table: The large flat facet on the very top.
- Crown: The upper portion above the girdle.
- Girdle: The widest part of the stone that the setting holds.
- Pavilion: The lower portion that reflects the light back up to the eye.
- Culet: The sharp point (or small facet) at the bottom.
The Physics of Sparkle
The secret to a "living" gemstone is Total Internal Reflection. A master faceter must calculate the pavilion angles based on the mineral's Refractive Index (RI).
- For Quartz (RI 1.54), the pavilion angle should be around 43 degrees.
- For Diamond (RI 2.42), it can be much shallower at 40.7 degrees.
If the angles are too shallow, the light leaks out the bottom (a "window"), making the stone look dead in the center.
Equipment and Precision
Faceting requires a specialized machine with an index gear (typically 64 or 96 teeth) and a precision protractor. Every facet is cut to a specific degree and a specific index number. This level of mathematical precision is what makes a faceted gem the pinnacle of the lapidary arts.