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Information on Uncut Gemstones

Here at Harriet Kelsall Bespoke Jewellery, we have been experimenting with setting uncut or rough diamonds. This produces a facinating effect for an engagement ring and we would encourage the daring amongst you to consider this as an option.

Diamond Cutting

Diamond Cutting is the art, skill and, increasingly, science of changing a diamond from a rough stone into an attractive gem. It is possible only because the hardness of diamond varies widely according to the direction in which one is trying to cut or grind.

'Cut' has two meanings in relation to diamonds. The first is the shape: round, oval and so on. The second relates to the specific quality of cut within the shape and the quality and price will vary very greatly based on the cut quality.

For all shapes ('cuts') of diamond, the cutter has two objectives which often conflict: to preserve the greatest possible amount of the weight of the rough diamond and to produce a cut which is both attractive and highly valued by the marketplace. The initial step is to choose the shapes of the final diamonds which will be produced from a particular piece of rough. This can be a very complicated choice, since it can involve tradeoffs to avoid inclusions (is more weight with this inclusion more or less valuable than lower weight without it?) or areas of less valuable color.

The history of diamond cutting and polishing has its origins in India, where it was discovered a long time ago by Indian lapidaries that a diamond could be made to glisten simply by grinding another diamond against it.

Nowadays the diamond and its powder play an important role in the cutting and polishing of diamonds. Over time modern machinery has replaced traditional diamond cutting tools.

Diamond cutting and polishing requires anywhere from several hours to several months to complete. During this process, a diamond will lose on average half of its original weight.

As every diamond is different, a stone must first be carefully examined by the cutter and then marked for cutting. Of all the cuts, the most popular is the round brilliant because of its ability to give a stone the greatest possible brilliance and fire with the most minimal amount of weight loss. The following cutting and polishing procedures uses the round brilliant cut as an example.

The rough diamond is divided into two parts by sawing or cleaving. Most stones are sawn across the 'grain' (visible evidence of the diamond's crystal structure) by a paper-thin metal disc coated with diamond dust revolving at high speed or by laser. The stones that are marked for cleaving are split along the grain by a single blow from a steel blade.

After cleaving or sawing, the corners of the diamond are rounded off by a process known as bruting or girdling (only round brilliant cuts require this step). The stone is cemented into a 'lathe', a holder that fits on a turning shaft. Another diamond is cemented to the end of a long rod held under the bruter's arm. As the lathe rotates, the two diamonds are brought together and grinded to shape. Diamond dust is produced from this action and is used in further sawing and faceting.

The brilliant now has a girdle-a sort of rim at the widest part by which it is usually set. The size or position of the girdle should not change throughout the rest of the diamond cutting process.

Diamond polishing

The polishing of the diamond begins; one by one, facets will be ground on to the stone. A facet is the tiny plane or surface that traps the light and makes a diamond sparkle. Most diamond cuts have 58 facets. The facets are applied to the diamond on a "turntable", made of porous iron, which has been coated with diamond dust and oil. The diamond is set into a holder and held against the turntable as it revolves at a very high speed.

A diamond has been cut well when its facets are clean, sharp, and symmetrical, and the proportions above and below the girdle are correct. A diamond is correctly proportioned when one-third of the total weight of the gem is above the girdle and two thirds below. A well-cut diamond will be fiery, brilliant and beautiful.

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