The history of the gemstone laboratories

Clarity
The purity of polished diamonds. The stone can have both internal and external characteristics. The inside usually consists of glitches (internal cracks), carbon residues that are not fully crystallised or nitrogen inclusions. They occur in all kinds of forms but also in various degrees of intensity. These are growth lines that show the structure of the raw stone.

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There are also external characteristics such as “beard”, which remains when the stone has been cut too hard, and “nerve”, which remains when the stone has been cut too sparingly. Both characteristics can be seen on the rim. All these characteristics determine the purity of the stone, which is classified in different categories: LC, VVS1, VVS2, VS1, VS2, SI1, SI2, P1, P2, P3. The assessment is always done visually with a magnifying glass and under a lamp that emits a light equivalent to daylight. The magnifying glass has a magnification of 10 and is an achromate, free of spherical and chromatic aberrations. This means that the diamond can be seen through the lens of the magnifying glass in full sharpness and without colour deviations.

Der Blaue Wittelsbacher, a 31 carat Fancy Deep Blue 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. 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.

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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.

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.

Gemstone laboratories
Gemstone laboratories are exclusively concerned with the evaluation of polished gemstones. The four “C’s” described above are assessed using the most modern means and techniques. The end result is laid down in the certificate on which the details of the four assessments are stated with as extra assessment the “Finish Grade”, which plays an extra role in larger 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.

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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.

Famous diamonds
Promise of Lesotho: 603 carats. One of the largest unprocessed diamonds ever found.
Centenary diamond: after cutting 273,88 carats, found in 1986.
Cullinan I or Star of Africa: 530,20 carats. Obtained from the Cullinan, with 3106 carats it is the largest rough diamond ever found.