The IDC (International Diamond Council) | Unsaid Library

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.

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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.

The colour of the diamond

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). There are also electronic assessments possible, for example by a photo spectrometer.

The IDC (International Diamond Council) uses the following colour scheme:

Gemstone laboratories deal exclusively with the assessment of polished gemstones. The four “C’s” described above are assessed using the most modern means and techniques. The end result is recorded in the certificate, on which the details of the four assessments are mentioned, with as an extra assessment the “Finish Grade”, which plays an extra role in case of higher and higher qualities. The certificate has a number that refers to the worksheet on which the stone is identified and graduated. This number is placed in the circle with a laser. A microphoto is made of the certificate. This microphoto is “sealed” at the same time as the stone.

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Certified stones are also often used as part of an investment portfolio and disappear into a safe to be re-traded at a later date. If the stone is removed from the seal to be used in jewellery, the stone can be identified at a later date on the basis of the number and worktop and then re-sealed.

Some examples of laboratories are: Hoge Raad voor de Diamant (HRD), Dutch Gemstone Laboratory, International Gemological Institute (IGI), Gemological Institute of America (GIA). In 2012, the High Council for Diamonds discovered fraud in certificates. Certificates were forged so that diamonds could be sold at higher prices.

Diamonds are formed under high pressure at a depth of between 140 and 190 kilometres in the earth’s mantle by compressing carbon. They are brought to the earth’s surface by rapid transport by means of explosive volcanoes. The volcanic rock has a characteristic blue colour and is called kimberlite after the place Kimberley in South Africa. In the nineties of the 20th century there was a diamond rush in northern Canada after the discovery of a kimberite pipe with economically recoverable diamonds in Lac de Gras in 1991.

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In addition to deposits in kimber loopt pipes and their immediate surroundings, diamonds also occur in alluvial deposits. In India, the delta of the river Krishna was traditionally the site of alluvial diamonds. Alluvial diamonds are also found in the Sperrgebiet south of Lüderitz on the coast of Namibia and in the adjacent coastal area of South Africa. In these areas, diamonds can be found in a sand layer up to a few metres below the surface.