For anyone involved in the diamond industry—whether a jeweller, designer, or buyer—knowing the proper terminology is essential for evaluating the quality and characteristics of diamonds. This glossary covers crucial terms used from the initial design and cutting processes through to the final assessment and craftsmanship of diamonds, ensuring you can make informed decisions about diamond quality, shape, clarity, and more.
4 Cs:
The four key aspects used to assess a diamond’s quality: Cut, Colour, Clarity, and Carat weight. These are essential factors in determining a diamond’s value.
60/60 Diamonds:
Round diamonds with a table and depth percentage around 60%. This combination generally enhances the return of white light over coloured fire.
Abrasion:
A worn or unpolished area on a diamond’s surface, usually found at facet junctions, as a result of wear.
AGS Grading Scale:
A diamond grading system from the American Gem Society (AGS), ranking cut, clarity, and colour on a scale from 0 to 10, with 0 representing ideal quality.
Angular Spectrum Evaluation Tool (ASET):
A tool used to assess a diamond’s light performance, including light return, contrast, and leakage, particularly helpful in evaluating cut quality.
Artisanal Mining:
Small-scale, labour-intensive mining, where individual miners dig for diamonds using simple tools. It is often conducted in challenging conditions and can have significant social impacts.
Azimuth:
A term used in diamond cutting to measure the direction a facet is pointing, essential in ensuring symmetry and proper light reflection.
Baguette Cut:
A step-cut rectangular diamond often used as an accent stone in jewellery, known for its elongated shape.
Bearding (Bearded Girdle):
Tiny hairline fractures around the girdle of a diamond, typically caused during the cutting process, which can affect the durability of the stone.
Bezel:
A facet on the crown of a diamond, situated between the table and the girdle. It can also refer to a setting that surrounds the diamond to secure it in place.
Blemish:
Any external imperfection on the surface of a diamond, such as scratches, nicks, or abrasions, which can affect the clarity grade.
Bow Tie Effect:
A shadow that appears across the centre of some fancy-shaped diamonds, such as ovals and pears, caused by improper light reflection.
Brilliance:
The intense white light reflected from a diamond, contributing to its overall sparkle and visual appeal. Brilliance results from the quality of the cut and polishing.
Brilliant Cut:
The most popular cut style, featuring 57 or 58 facets designed to maximise a diamond’s brilliance and light return. The round brilliant cut is the most common.
Bruise:
A tiny area of damage that occurs at the surface of a diamond, often accompanied by small feather-like inclusions extending into the stone.
Carat:
The standard unit of weight for diamonds, where 1 carat equals 200 milligrams. Carat weight is often associated with size, but dimensions can vary depending on the cut.
Cavity:
A large or deep inclusion on a diamond’s surface, usually formed when part of the crystal breaks away during cutting or polishing.
Chevron:
V-shaped facets on the pavilion of a princess cut diamond, which can enhance the sparkle by increasing light return.
Chip:
A small, shallow break in the diamond’s surface, usually occurring near facet junctions or along the girdle due to accidental damage.
Clarity:
A grading of a diamond’s internal and external imperfections. Clarity ranges from flawless (no visible imperfections under 10x magnification) to included, where flaws are easily visible.
Cloud:
A cluster of tiny inclusions that appear as a hazy or cloudy area within the diamond, potentially affecting clarity.
Conflict Diamond:
Diamonds mined in areas controlled by rebel groups and sold to fund armed conflict against governments. The Kimberley Process was introduced to prevent the sale of conflict diamonds.
Crown:
The upper part of a diamond, located above the girdle, including the bezel facets and table. The crown plays a significant role in the diamond’s overall brilliance.
Crown Angle:
The angle between the bezel facets and the girdle plane. This angle affects the diamond’s light performance, including how much light enters and reflects from the crown.
Culet:
The small facet at the bottom of a diamond’s pavilion. A pointed culet offers no visible facet, while a larger culet may appear as a small circle or hole when viewed from above.
Cushion Cut:
A square or rectangular-shaped diamond with rounded corners, offering a vintage appearance. Cushion cuts often have larger facets that highlight the diamond’s clarity and fire.
Depth:
The vertical measurement from the table to the culet of a diamond. Depth percentage is important in determining how well the diamond reflects light.
Dispersion (Fire):
The prismatic effect in diamonds that separates white light into a spectrum of colours, creating the coloured flashes (fire) visible in well-cut stones.
Feather:
An internal inclusion that resembles a crack. Feathers can vary in size and visibility, and they may affect the diamond’s durability if located near the surface.
Fluorescence:
The visible light some diamonds emit when exposed to ultraviolet (UV) light. Fluorescence is often blue, and while it doesn’t always affect the appearance, strong fluorescence can make a diamond appear hazy in daylight.
Girdle:
The outer edge of a diamond at its widest point, separating the crown from the pavilion. Girdles can be polished, unpolished, or faceted and vary in thickness.
Inclusion:
Any internal imperfection within a diamond, such as crystals, feathers, or clouds. Inclusions are an essential factor in determining the clarity grade.
Knot:
A type of inclusion where an internal crystal extends to the surface of the diamond, often visible at facet junctions.
Laser Drilling:
A treatment used to remove or reduce the appearance of inclusions. The process involves creating tiny tunnels in the diamond with a laser, allowing access for further treatments.
Marquise Cut:
An elongated diamond with pointed ends, known for its boat-like shape. The marquise cut creates a long, elegant appearance and maximises carat weight.
Melee:
Small diamonds, usually less than 0.20 carats, often used as accent stones in larger jewellery pieces.
Needle:
A long, thin crystal inclusion that appears as a line within the diamond. Needles are usually only visible under magnification and can affect clarity.
Pavilion:
The lower part of a diamond, located below the girdle. The pavilion’s angle and depth are critical in determining how light is reflected through the diamond.
Pinpoint:
A tiny, dot-like inclusion, often visible under magnification. When grouped together, pinpoints can form clouds that affect a diamond’s clarity.
Princess Cut:
A square or rectangular diamond cut that features brilliant-style faceting. Known for its sharp corners and fire, the princess cut is a popular alternative to round diamonds.
Scintillation:
The flashes of light that a diamond emits when it moves or when the light source shifts. Scintillation is a key component of a diamond’s sparkle.
Star Facet:
The small triangular facets on a diamond’s crown, located between the bezel facets and the table.
Table:
The largest, flat facet on the top of a diamond. The size of the table affects the diamond’s brilliance and fire.
Twinning Wisp:
A cloudy or thread-like inclusion formed during the diamond’s growth, often associated with crystal distortion. Twinning wisps can be a combination of pinpoints, clouds, or crystals.
