What is the Cullinan Diamond? | Unsaid Library

The Cullinan diamond

The Cullinan is the largest uncut diamond found on earth so far: 3106 carats (621.2 grams). The Cullinan was cleaved and cut and the largest piece, the Cullinan 1 (530.20 carats) was the largest cut diamond for about a century after it was cut. The largest cut diamond since 1988, however, is the Golden Jubilee (545.67 carats), which was cut by Gabriel (Gabi) Tolkowsky on behalf of De Beers and has been in the possession of the Thai king Bhumibol since 1997, who received it on the occasion of his 50th coronation jubilee.

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Many diamonds for industrial purposes are also made synthetically. Synthetic diamonds can only be distinguished from natural diamonds in a laboratory. Researchers from the Carnegie Institution of Washington discovered in 2004 a process to synthesize within 24 hours diamonds that are more than 50% harder than natural diamonds.

Diamond is the hardest material found in nature. There are only two (industrially manufactured) materials that are harder, namely aggregated carbon nanorods and ultrahard fullerene. Like diamonds, these are made up of carbon atoms. Diamond itself is a transparent crystal with a very high refractive index (2.417) and a high dispersion (0.044). In jewellery, the (sun) light is therefore brilliantly broken and reflected depending on the shape of the cut. In addition, the polished polished surface of the diamond stone does not become matt due to its high hardness.

Because of its extreme hardness, diamonds are used in industry, for example for grinding, drilling, cutting and polishing and wire drawing. A diamond owes its hardness to its tetrahedron structure and is therefore harder when it contains fewer inclusions or crystal lattice defects. Diamond is relatively brittle due to its hardness. In vacuum, diamonds are transformed into graphite at a temperature of 1700°C and into air at a temperature of 700°C.

Besides the hardness, the thermal conductivity (410 W/cm/K) and the (electrical) resistance of 1013 Ω-m of diamond are also very high. This combination makes that diamonds can be used in electronic circuits to dissipate heat. Diamond behaves like silicon as a semiconductor and in liquid helium as a superconductor, as discovered in 2004.

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Rough diamonds are processed to break the light brilliantly. After processing, a stone is left with a sparkle and a play of colours, which is assessed on various criteria to arrive at a price. The criteria are the 4 C’s and include:

Cut
This is understood to mean the creation of the stone. The shape in which the stone is cut is a part of this. The product relates to the quality of the grinding and the proportions of the grinding form. The essence lies in the right “proportions” and the “refinement” of the cut stone. The proportions include the height of the crown, the crown angle, the depth of the pavilion side, the table reflection and the ratio of the roundness to the total depth of the stone.

Refinement is understood to mean the precise finishing of the total product. How regular is the round-distant, is the column heavy or light, are there symmetry differences between the crown and the pavilion side, do the facets fit straight together, is the column exactly in the middle or is the table decentralized?

All these things have a direct influence on the play of light in the stone. The product is human, in contrast to the purity, colour and partly the weight. It is therefore a major price determining factor in the four “C”‘s: a stone with a nice round weight, flawless and the highest colour in a brilliant cut may look like a top stone, but if the stone is cut too deep (nail) or too shallow (fish eye) then the light play in the stone is dead and the stone has a lower value.

How a colour diamond is judged is rather subjective. A pure diamond is colourless. Usually, the less color, the purer, so the more valuable it is. Certain relatively common discolourations, such as yellow, reduce the value of the diamond. Of course these stones remain valuable; in 2011 a yellow diamond was auctioned for about 8 million euros. Less common colours such as pink and blue on the other hand increase the value; in 2010 a pink diamond yielded the record amount of 34 million euros. Black diamonds, which may be of extraterrestrial origin, are also rare. In 2011 and 2012, scientists discovered for the first time celestial bodies that according to them consist mainly of diamonds, although the claim from 2011 is disputed.

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The colour is determined on the basis of a set of so-called calibration stones (the so-called masterstones). This is a collection of stones judged by several leading diamantairs with different colors in the highest grades, which are considered standards. The assessment is usually done visually (with the eye).