The 31 carat Fancy Deep Blue diamond

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.

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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.

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. Together with 104 other stones cut by the Diamond Cutter Asscher in Amsterdam in 1908. Decorates the sceptre of the kings of England. It is kept in the Tower of London. This was until 1997 the largest cut diamond.
Cullinan IV: 63,60 carat. One of the 105 stones cut from the Cullinan. Located in the crown of Queen Mary. Can also be taken from the crown and worn as a brooch. It is kept in the Tower in London.
Darya-ye Noor (sea of light): estimated 182 carats, from India, owned by Iranian government.
Dresden green diamond: 41.00 carat, probably from India, earliest history not known. In 1742 by Friedrich August II, Elector of Saxony, bought for 400 000 talers. It is kept in the Grünes Gewölbe in Dresden.

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Florentiner or Toscaner: 137.27 carats, Early history surrounded by legends. In 1657 in the possession of the Medici in Florence, In the 18th century in the crown of the Habsburgs, then used as a brooch.
Hopediamond: 45.52 carats, appeared in 1830 on the market and was bought by banker H.Ph. Hope. Probably recut from a stolen stone. Also part of the French crown jewels. Since 1958 at the Smithsonian Institution in Washington.
Koh-i-Noor: 108,93 carats. Originally in round form with 186 carats owned by Indian monarchs. Acquired in 1739 by the Shah of Persia. Later came into the possession of the British East India Company, which donated it to Queen Victoria in 1850. He was first given a place in the crown of Queen Mary, wife of George V, and later in the crown of Queen Mother Elizabeth. It is kept in the Tower of London.
Nassak: 43.38 carats. Originally more than 90 carats, was located in India in a Shiva temple near Nassak. Acquired by the British in 1818 as a war booty. In 1927 cut in New York. Now in private possession in the United States.