How do they determine the colour and quality of a diamond? | Unsaid Library

Judging 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.

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. These areas are closed to anyone who has no business there. Part of the diamond is also washed into the Atlantic Ocean and is mined there by diamond fishermen.

High-pressure subduction zones may function as an alternative parent rock for diamonds. In the Beni Bousera massif in northern Morocco, micro diamond associations have been found that point in that direction.

The table below shows an overview of the diamond production since 2006. In 2009 production decreased by about 20% as a result of the credit crisis. Production has not yet recovered to pre-crisis levels. Until 2007 South Africa was the fifth largest producer worldwide, but in that year it was pushed to the sixth position by Canada. In 2016 the average value of a carat rough diamond was US$ 92.50. Diamonds with the highest value per carat were mined in Lesotho, average value over US$ 1000, and in the Democratic Republic of Congo (DRC) this was only US$ 10. The latter country had a share of 17% in global production in volume terms, but in value terms this share was 2%.

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The Russian company ALROSA, active in the republic of Yakutia, is the largest producer of diamonds in the world with 28% of world production. De Beers, for a long time, had been virtually a global player.

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