STAGES IN FACETING A BRILLIANT DIAMOND

The four main diamond-cutting centres in the world are Antwerp, Mumbai (India), New York City, and Tel Aviv. Although much of the process can now be carried out with the aid of computers, there is still a need for the 'eye' of the expert to check the progress and assess the accuracy, make, and overall look of the gemstone.

Stage 1 The designer will decide how best to use the shape of the rough stone, taking into account any flaws or inclusions, the weight, and the overall quality of the stone. The designer may be looking to produce the largest stone possible, or several smaller stones with a larger combined weight. There will usually be a compromise between the number and size of the stones that could be produced and the final yield. The value and quality of the polished diamond will be judged on its colour, cut, clarity, and carat (weight) - the 4C's.

Stage 2 Once the decision has been made how best to use the rough stone, it is marked for the first cut (saw) or cleavage (a break along a plane of weakness related to the atomic structure of the dia­mond). Nowadays, diamond sawing can be carried out by in a facto­ry by computer controlled lasers.

Stage 3 The first step in faceting an octahedral diamond crystal may be to saw off the top of the crystal using a rotating disc coated with a coarse diamond abrasive. A diamond may also be cleaved to divide it in two. In order to cleave a diamond, the diamond is first cemented to a stick (dop), a small groove (kerf) is made along the mark into which is placed a steel blade. The blade is then given a sharp hit with an iron bar to cleave the diamond in two.

Stage 4 The diamond is given a rounded outline by holding it against a revolving cast-iron wheel, known as a 'scaife', coated with a diamond powder paste. This process, called bruting, gives the diamond the appearance of frosted glass. The girdle, the widest part of the stone, which will separate the top (crown) facets from the lower (pavilion) facets, can be seen at the end of this stage.

Stage 5 The facets are then made using the scaife. The flat table facet is ground first and then the bezel facets. The facets are ground and polished in a particular order; first the pavilion main facets, the culet, star facets, upper girdle facets and lower girdle facets. Stage 6 A 'brillianteer' then adds the remaining 24 crown and 16 pavilion facets, bringing the total to 58 facets including the culet. A finer-grained diamond abrasive powder is used for each progres­sive stage of polishing. The diamond is then ready to be mounted in a ring or other piece of jewellery.