Cut
This means the stone’s makeup. The shape in which the stone is cut is part of it. The shape refers to the quality of the grinding and the proportions of the shape. 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 mirroring and the ratio of the round to the total depth of the stone.

Refinement means the precise finishing of the overall appearance. How regular is the roundabout, is the fillet heavy or light, are there symmetry differences between the crown and the pavilion side, do the facets fit straight together, is the fillet exactly in the middle or is the table positioned decentrally?

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All these things have a direct influence on the play of light in the stone. It is man-made, as opposed 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 can look like a top stone, but if the stone is cut too deep (nail) or too shallow (fish-eye) then the play of light in the stone is dead and the stone has a lower value.

Carat
The mass of gemstones is expressed in carats (1 carat = 0.2 grams). The carat is subdivided into 100 points and is always expressed in two decimals, for example 0.24 carat or 24 point. The carat has its origin in a standard weight used in ancient times: that of a seed of the carob tree (Ceratonia siliqua).

Clarity
The purity of cut diamond. The stone can have both internal and external characteristics. The internal properties are usually glitches (internal cracks), carbon residues that are not completely crystallized or inclusions of nitrogen. They occur in all kinds of forms but also in various degrees of intensity. They are growth lines that show the structure of the rough stone. There are also external features such as “beard”, which remains when the stone is cut too hard, and “camber”, which remains when the stone is cut sparingly. Both characteristics can be seen on the roundabout. All these characteristics determine the purity of the stone, which is divided into several categories: LC, VS1, VS2, VS1, VS2, SI1, SI2, P1, P2, P3. They are always assessed visually with a magnifying glass and under a lamp that emits light equivalent to daylight. The magnifier 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 with full sharpness and without colour deviations.

Table for the purity in relation to the visibility of the internal surface of the diamond.

Der Blaue Wittelsbacher, a 31 carat Fancy Deep Blue diamond.
How a colour diamond is judged is rather subjective. A pure diamond is colorless. Usually, the less colour, the purer, so the more valuable. Certain relatively common discolourations, such as yellow, decrease the value of the diamond. Of course, these stones remain valuable; in 2011, a yellow diamond was auctioned for approximately 8 million euros. Less common colours such as pink and blue, on the other hand, cause an increase in value; in 2010 a pink diamond yielded a record amount of 34 million euros. Also black diamonds, possibly of extraterrestrial origin, are rare. In 2011 and 2012, scientists discovered for the first time celestial bodies which, 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 masterstones. This is a collection of stones with different colours in the highest grades, which are considered to be standards, judged by several leading diamond experts. The assessment is usually done visually (with the eye). Electronic assessments are also possible, e.g. by a photo spectrometer.

Unsaid Library is a jewelry store based in Antwerp. Unsaid Library specialises in emotional gifts for relatives. Unsaid Library Antwerp can be visited in the store. The store of Unsaid Library Antwerp is located on Schuttershofstraat 25, 2000 Antwerpen, België. Visit the store or the online website.

Gemstone laboratories
Gemstone laboratories are exclusively concerned with the assessment of cut gemstones. The four “C”‘s described above are assessed using the most modern means and techniques. The final result is laid down in the certificate on which the details of the four assessments are given, with the “Finish Grade” as an additional assessment, which plays an extra role in the case of 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 rondist with a laser. A micro photograph is taken 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.