Faceting is the art of cutting gemstones to reveal their natural beauty through a precise arrangement of polished surfaces, or facets. Mastery of this terminology is invaluable for jewellers, gemologists, and enthusiasts who seek to understand the nuances of gemstone design and the craftsmanship behind each cut. This glossary provides essential terms used throughout the faceting process, making complex techniques and terminology accessible for both beginners and seasoned professionals.
Acetone
A solvent commonly used to dissolve dop wax or release adhesives used in the faceting process.
Alignment
The precise positioning of a gemstone so that corresponding facets on the crown and pavilion match at the girdle.
Analog Angle Scale
A protractor-based scale on some faceting machines that allows manual adjustment of angles, typically accurate to a tenth of a degree.
Axis
Refers to lines in a gemstone along which it can be cut, including the A-axis (width), B-axis (depth), and C-axis (length), which influence the orientation of facets.
Boule
A cylindrical synthetic gemstone, often created through flame fusion processes, is used as an affordable alternative to natural gemstones.
Brilliance
The degree of light reflection within a faceted gemstone, is impacted by factors like cut, polish, and the gem’s refractive index.
Caliper
An instrument used to measure the dimensions of a gemstone accurately.
CAM (Centre Point Angle Method)
A faceting technique that establishes a stone’s initial shape by creating temporary pavilion facets and corresponding girdle facets.
Carat
A unit of weight for gemstones, where 1 carat equals 200 milligrams or 1/5 of a gram.
Charging
The process of applying a polishing compound, often diamond grit, onto a lap.
Cheating
A minor adjustment of facet angles to ensure precise meets between facets, commonly done after initial polishing.
Cleavage and Fracture
Terms describing how a gemstone breaks; cleavage refers to breaking along flat planes, while fracture describes irregular breaks.
Colour Absorption
The specific wavelengths of light absorbed by a gemstone, contribute to its visible colour.
Colour Zoning
Variations in colour within a gemstone, are often seen in layers or patches due to natural mineral growth.
Crown
The top portion of a gemstone above the girdle, is typically polished to enhance the gem’s sparkle.
Critical Angle
The angle at which light enters a gemstone is entirely reflected within it, is critical for maximising a stone’s brilliance.
Culet
The bottommost facet or point of a gemstone’s pavilion, is sometimes flat to reduce the risk of chipping.
Depth
The distance from the table (top) to the culet (bottom) of a gemstone, is a key factor in determining light performance.
Dop
A metal rod or holder to which a gemstone is attached with wax or adhesive for cutting on a faceting machine.
Dopping
Attach a gemstone to a dop stick, typically with wax or epoxy, to hold it securely during cutting.
Double Refraction
A phenomenon in certain gemstones where light splits into two paths, creating a doubling effect of facets when viewed through the stone.
Facet
A flat, polished surface on a gemstone, each precisely angled to enhance light reflection and dispersion.
Faceting Head
A component of a faceting machine that holds and positions the dop stick and allows adjustment of angle and index settings.
Fish-eye
An optical effect where a gemstone appears lifeless or “dead” when pavilion angles are too shallow, allowing light to escape.
Girdle
The outer edge or boundary between a gemstone’s crown and pavilion, provides a mounting point for settings.
Index Gear
A toothed gear on a faceting machine controls the rotation angle of the gemstone to create evenly spaced facets.
Keel
A continuous line or edge at the base of a gemstone’s pavilion, typical in shapes like emerald cuts.
Lap
A flat, rotating disk covered in an abrasive substance used for cutting and polishing gemstones.
Loupe
A magnifying device, typically 10x magnification, is used by jewellers to inspect a gemstone’s facets and polish quality.
Meet Point
The junction of two or more facets, where precise alignment is crucial for achieving symmetry in the gemstone’s design.
Mohs Scale
A scale of hardness is used to classify gemstones from 1 (softest) to 10 (hardest), indicating their scratch resistance.
Pavilion
The lower section of a gemstone, below the girdle, is designed to reflect light back through the crown.
Polish
The final finish of a facet’s surface impacts a gemstone’s brilliance and quality of light reflection.
Quill
The component on a faceting machine that holds the dop stick, allows the stone to be angled for cutting.
Refraction
The bending of light as it enters or exits a gemstone influences the gemstone’s colour and brightness.
Refractive Index (RI)
The measure of light refraction within a gemstone determines how light bends and travels through it.
Scintillation
The “sparkle” effect in a faceted gemstone, is created by light reflecting off multiple facets.
Symmetry
The alignment and uniformity of facets on a gemstone, affect its visual appeal and value.
Table
The largest, flat facet on the crown of a gemstone, is positioned parallel to the girdle to maximise light entry.
Tier
A row or series of facets on the crown or pavilion at the same angle and elevation relative to the girdle.
Ultralap
A thin, flexible lap coated with fine polishing compounds is used to achieve a high polish on gemstone facets.
Vernier Scale
A measurement tool on some faceting machines that allows precise angle adjustments for the quill, often to a tenth of a degree.
Vertical Axis
An imaginary line running through the centre of a gemstone, from the table to the culet, is used as a reference in faceting.
