Glossary

Baguette

A step cut in the shape of a small rectangular stone which may be tapered at one end.

Carat Weight

The standard unit of weight for diamonds and most other gems. One metric carat equals 0.200 gram. If all other factors are equal, the more a stone weighs, the more valuable it will be.

Clarity

Clarity is a diamond's relative position on a scale ranging from 'flawless' to 'imperfect'. Characteristics of clarity are classified as inclusions (internal) or blemishes (external). The clarity grade is determined by the size, number, position, nature, and colour or relief of characteristics. When all other factors are equal, flawless stones are the most valuable.

Clarity Enhanced Diamonds

Diamonds which have fractures or large inclusions can be improved by having these features disguised or removed. These are called "clarity enhanced diamonds" and should be disclosed as such when being sold. The main methods of clarity enhancement are Fracture Filling and Lasering, which are described under separate headings.

Colour

Grading colour in the normal range involves deciding how closely a diamond's body colour approaches colourlessness. Most diamonds have at least a trace of yellow or brown body colour. With the exception of some natural fancy colours, the colourless grade is the most valuable.

Crown

This is the upper part of the diamond above the girdle and consists of a large flat area on top, known as a table, plus several facets below it.

Cut

Also known as the 'make', the cut represents the proportions and finish of a polished diamond. Cut can also mean shape, as in emerald cut or marquise cut. The cut affects both the weight yield from rough and the optical efficiency of the polished diamond. The more successful the cutter is in balancing these considerations, the more valuable the diamond.

Emerald cut

A step cut, usually rectangular, with cut corners. This is a cut which accentuates colour and clarity rather than aiming to maximise sparkle.

Facet

A facet is a plane, polished surface of a diamond....

Fancy Diamond

A fancy diamond is one with an attractive natural body colour other than light yellow or light brown. Red, blue and pink diamonds are examples.

Flaw

An imperfection in a diamond.

Fracture

A crack inside a diamond, sometimes coming to the surface.

Fracture filled diamonds

When a diamond has a fracture that comes to the surface, it can be improved by a process known as "fracture filling". A liquid of high refractive index is forced under temperature and pressure into the fracture plane and the fracture is disguised but not altogether hidden. The glassiness of the filling causes a purple colouring to be exhibited when viewed at certain angles, something never present in natural diamonds. When a fracture filled diamond is offered for sale, it should be disclosed as clarity enhanced.

Girdle

The girdle is the outer edge or the widest part of the diamond that forms a band around the stone.

Hardness

Hardness refers to a mineral's resistance to scratching on a smooth surface. The Mohs scale of relative hardness consists of 10 minerals, each scratching all those below it in the scale and being scratched by all those above it. The scale is an arbitrary one. The hardness of diamond is 10, followed by ruby and sapphire at 9, followed by topaz at 8. However, diamond is approximately 140 times harder than ruby and sapphire which in turn are approximately 5 times harder than topaz.

Inclusion

An imperfection internal to the Diamond.

Internal Graining

Internal indiciations of irregular crystal growth. They may appear milky, like faint lines or streaks, or may be colored or reflective.

Irradiated diamond

A diamond that has been exposed to radiation in order to improve either its colour or clarity. An irradiated diamond should be disclosed as such if offered for sale.

Lasering

Any large unsightly inclusions in a diamond can be effectively removed by a process known as lasering. A lasered diamond can be detected since the "drill hole" from the surface of the diamond to where the inclusion was is often visible under a lens and looks like a small tube.

When a lasered diamond is offered for sale it should be disclosed as 'clarity enhanced'.

Loupe

A magnifying glass usually of 10X magnification.

Melee

Small Diamonds under .20 carat.

Mohs scale

This is the ten point scale of mineral hardness keyed to the following minerals:

   1. Talc
   2. Gypsum
   3. Calcite
   4. Fluorite
   5. Apatite
   6. Orthoclase (feldspar)
   7. Quartz (citrine and amethyst)
   8. Topaz
   9. Corundum (ruby and sapphire)
  10. Diamond

This scale is neither linear nor in a particular ratio. Diamond is approximately 140 times harder than corundum which is approximately 5 times harder than topaz.

Pavilion

The pavilion is the bottom part of the Diamond, below the girdle.

Round Brilliant cut

This is the most common cut applied to a diamond and comprises 58 facets. It is the cut which makes the most efficient use of light to maximise brilliance (sparkle) and dispersion (fire).

Spread stone

A diamond with a large table and a thin crown height. Such a diamond will appear large but lack sparkle.

Treated Diamond

A diamond whose body colour has been induced by some form of artificial irradiation. This is often done in conjunction with controlled heating, a process known as annealing.