The diamond rating system was rigorously developed by the US-based Gemological Institute in the mid-1930s. It was introduced for use on a global scale in 1953. The basis of the evaluation of diamonds are four quantities, determined in specially equipped gemological laboratories, which include:
cut – in English: cut,
color – in English: color,
purity – in English: clarity,
weight – in English: carat
Cut – the cut of a diamond has been developing for a very long time and documents that grinding a natural diamond creates a brilliant. The basic form of the diamond has a circular shape. It is cut into 57 facets, of which 33 are located in its upper part – the crown and 24 in its lower part – the pavilion. The role of the crown is to scatter light on different colors of the spectrum. We call this phenomenon dispersion. The task of the pavilion is to bounce the light back into the crown. The assessment of the quality of the cut is based on the overall impression that the beauty of brilliance evokes in the assessor and at the same time in the client.
Color – is determined by visual evaluation using a special lamp on an ultra-white background and in daylight. The colors are determined as follows: colorless – they fall into groups D, E, F; almost colorless – group G, H, I, J; group yellowish to brownish K, L, M (tinted grade 1); group very light yellow to very light brownish – N, O, P, Q, R (tinted level 2); group light yellow to light brown – S, T, U, V, W, X, Y, Z – (tinted level 3). A special group consists of colored diamonds – pink, red and blue, known under the trade name “fancy”. They are very rare and extremely expensive.
Clarity – expresses the degree of internal defects of the diamond – inclusions of other minerals, liquids, gases, cracks, fissures, turbidity, cavities, etc. The degree of purity is determined using a jewelry magnifying glass with 10x magnification. All of the above internal flaws, but especially inclusions, reduce the brilliance of the diamond. The American Gemological Institute (GIA) classifies gemstone diamonds into the following groups according to their purity.
Clean under the magnifying glass; very, very small inclusions; very small inclusions; small inclusions; moderate inclusions; larger inclusions; large inclusions.
The weight (Carat) – 4 C of gemstones was adapted to the metric system at the beginning of the 20th century. One carat (mark ct. = 200 mg = 0.2 g). The weight of diamonds is given to two decimal places (when rounding up, it must be in thousands). Very small diamonds are listed in the so-called points. One point equals one hundredth of a carat – 0.01 ct. The term “mills” includes a group of stones from 0.07 to 0.14 ct. Stones weighing 0.12 – 0.15 ct are called “coarse”. A 1.00 carat diamond is called a “fourgrainer” and a 0.5 carat diamond is called a “twograiner”. A template with cut holes from 0.01 to 6.00 ct is used to roughly estimate the weight of the diamonds.
However, other Cs – Confidence, Certainty and Certificate – are important to the unwritten, especially in business practice.
