GLOSSARY OF TECHNICAL TERMS

Acidising:
refers to the treatment of diamonds with acids (usually hot) to clean them after mining or after cutting, particularly to remove oxides or polishing residues from surface fissures.


A jour :
is a type of diamond mount that exposes the pavilion to the light and is used in most modern mounts, unlike earlier closed settings.


Baguette:
refers to a diamond cut in the shape of a narrow bar, sometimes tapered at one end. It was named after the long French bread loaf.


Baton:
is another name for a baguette.


Bedrock:
is the solid rock found under deposits of gravels, silt, sand, soil, etcetera.



Bezel facets:
occur when the cross-cutter makes the four top corner facets into eight.


Bicycle tyre:
refers to a thick girdle.


Blocking:
is putting on the 16 main facets by the cross-cutter.


Blue ground:
is the miner's name for the unoxidised kimberlite in a pipe or other kimberlitic deposit.


Blue-white:
is a confusing term often wrongly applied. A blue-white stone should have a faint tinge of blue, even though the description is usually intended to mean colourless. Sometimes it is even applied to stones with a faint tinge of yellow.


Boart:
is a very low-grade diamond suitable only for industrial use. It is also spelt bort, boort, and bortz.




Brillianteerer:
is the skilled person responsible for the final stages of putting on and polishing the 40 facets after the cross-cutter's work. It is also spelled brilliandeer.


Brilliance:
is the intensity of the white light when a diamond is looked at in the face-up position.


Bruting:
is another name for cutting to fashion the girdle outline of a brilliant cut.


Calibré cut:
refers to stones that have been cut to standard dimensions for easy setting into standard mounts.


Carat:
is the standardised unit of weight for gemstones. One carat is equal to 0.20 of a gram.


Clean:
is used to describe a diamond that has no readily visible inclusions, grade SI and above.




Cleavage:
refers to the tendency of a diamond to split along the grain parallel to one of its octahedral faces. It is also a term applied to rough diamonds that have at some time been cleaved from a larger stone.


Cleaver:
is the skilled person who cleaves a diamond into two parts.


Closed culet:
is the sharp point at the bottom of the pavilion of a brilliant cut, or knife edge on an emerald-cut stone.


Cross-cutter:
is the skilled person who grinds and polishes the first 16 facets on a diamond.

Crown:
is the upper part of a polished stone above the girdle.

C.S.O.:
is the Central Selling Organisation which distributes about 80 per cent of the world's rough gem quality diamonds.




Culet:
refers to very small facet on the bottom of the pavilion, parallel to the table. It is also spelled collet and culette.


Cut:
is the shape into which a rough diamond is cut and polished.


Cutter or bruter:
makes the rough diamond round before it is faceted.

Diamond paper:
is another name for the parcel paper.

Diamond parcel paper:
is the specially folded paper in which a diamond is or diamonds are held for carrying, or transporting.

Dispersion:
describes the way a diamond breaks up a ray of white light into colour.

Dop:
refers to the holder used for a diamond that is being polished. A diamond is held in a solder dop by solder and in a mechanical dop by metal jaws.



Extraction:
describes the process of removing diamonds from concentrate.

Extra facet:
is an additional small facet usually applied to remove a small blemish most commonly on or near the girdle.

Extra facet:
is an additional small facet usually applied to remove a small blemish most commonly on or near the girdle.

Faceted girdle:
refers to a girdle on which small facets have been polished to improve the brilliance of the diamond.


Face up:
is the position of a diamond with the table of the stone facing the viewer.


Fancies:
are attractively coloured diamonds.


Fancy:
is a diamond of an attractive colour other than white that is suitable for gem use.

Fire:
refers to the flashing colours seen when a suitably cut diamond is moved, resulting from its dispersion.

Flute:
is a thin paper used to line the inside of a diamond parcel paper.

Full-cut brilliant:
is the correct name for a brilliant-cut diamond with 56 facets plus table and culet.



Girdle:
is a sort of rim at the widest part of a diamond by which it is normally set. It is the resulting circumference of the adjoining crown and pavilion angles at the widest part of the stone.

Girdling:
describes the way a rough diamond is rounded. It is also another name for cutting and bruting.

Grader:
is the skilled person who separates polished diamonds into sizes and quality grades by clarity, colour, and accuracy of cut.

Grain:
is a name used by cutters and polishers to describe the visible evidence of the crystal structure of a diamond, and will usually determine their procedure.

Loose diamond:
is an unmounted, polished diamond.

Loose diamond:
is an unmounted, polished diamond.

Lustre:
refers to the quality of a surface in reflected light. The lustre of a diamond is usually described as admantine lustre.

Mêlée:
are rough stones and shapes under two carats and used loosely for small polished diamonds.



Mixed-cut:
is the mixing of two different cuts for one diamond, such as a brilliant cut crown and step-cut pavilion.

Mount or mounting:
is the part of jewellery into which a stone is set.

Natural:
is part of the natural surface of a rough diamond left on the girdle by the cutter striving for maximum weight retention.

Navette:
is another name for a marquise.

Near-gem:
is a quality of rough diamonds between gem and industrial.

Octagon:
word describes the process of adding the eight main facets to the top and bottom of a stone, which makes its table octagon-shaped.

Open culet:
is a larger than normal culet.



Open table:
is a larger than normal facet.

Open cast or open pit:
describes mining from the surface.

Opening a diamond:
means polishing a window on a rough stone to see inside it.

Pavilion:
is the bottom part of a polished diamond below the girdle.

Pipe:
refers to a roughly funnel-shaped, usually extrusion of volcanic rock that may or may not contain diamonds.

Point:
is the hundredth of a carat, therefore 0.72 carats equal 72 points.

Polished girdle:
refers to a girdle that has been polished but not faceted.

Quality:
measures the degree of excellence of a diamond by its weight, colour, clarity and (polished) its perfection of cut.



Rough:
is the name given to diamonds before they are cut.

Sawyer:
is the skilled person who saw diamonds.

Sawable:
are the rough diamonds that can be divided by sawing.

Scaife:
is also spelled scaive or scaif, and refers to the horizontal turntable or grinding table on which a diamond is polished.

Scintillation:
refers to the flashing and twinkling sparkle of a diamond when it moved under light. A diamond is always more beautiful in motion because its scintillation depends upon the number of facets visible to the eye when the diamond moves.



Set:
is a diamond or other stone set in a mount.

Skin:
is the natural surface of the unpolished diamond.

Sorter:
is the skilled person who separates rough diamonds into sizes and grades of quality by shape, colour, and clarity.

Star facets:
are the eight triangular facets around the table of a diamond that make it star-shaped.

Table:
is the large facet on the top of the diamond's crown.

Treated:
describes a polished diamond that has been altered to change its appearance, eg by artificial colouration, that is, irradiation.

Window:
is the facet polished on a rough diamond in order to see inside it.