The value of a diamond is determined by 4 quality factors. These were established in Amsterdam in 1975, during the congress of the World Federation of Diamond Bourses (W.F.D.B.) and the International Diamond Manufacturers Association (I.D.M.A.). It became known as the system of the 4 C’s, after the words Carat, Colour, Cut and Clarity.
The larger the diamond and the finer the colour, the higher its value is; the greater the clarity, the more beautifully and better cut, the more perfect it is. The price of diamonds is kept stable by regulating what flows into the market. The world stock is supposedly large enough to provide a cupful of diamonds for every inhabitant of the USA.
The more colourless the stone, the more valuable the diamond. For only a very small number of diamonds are completely colourless. Most vary in very light hues from yellow to brown. Many other distinct colours also occur, the so-called fancy colours. Colour comes about as the result of chemical substances penetrating the atomic structure; these include nitrogen (yellow), magnesium (rose), radium (green) and borium (blue). Red is the rarest colour and therefore very costly. The colour of diamonds can be changed artificially by irradiation with electrons. The artificial colouring must be mentioned in the certificate for these diamonds: ‘Artificially coloured by treatment’. The colour of a diamond is determined by comparing the stone with ‘masterstones’. These are reference stones that correspond with the colour scale for diamonds which was established by international professional organisations in 1978. The fantasy colours, fall outside this framework.
In the course of the centuries, different types of cuts have come into existence, partly as a consequence of technological progress. Before 1400 the given crystal shape had been used, such as the octahedron - two pyramids with their bases together. Later, the better-reflecting table-shaped cut came into fashion. At the end of the 15th century, the Antwerp polisher Lodewijk van Berken invented the revolutionary polishing scaife. As a result of this it became possible to cut symmetrical facets. Thus in the 16th century the rose cut, with a limited number of facets, came into vogue in Europe. In the 17th century, diamonds were for the first time cut in the brilliant shape with its many facets. Depending on its proportions, the round brilliant with 57 facets is the ideal cut.
The way in which the stone is polished partly determines its value. In 1919, the famous diamond polisher Marcel Tolkowsky formulated the ‘ideal cut’. This cut has the ideal proportions for a brilliant. If the proportions are ideal and the facets have the correct form and dovetail together beautifully, the sparkle and fine (reflection and refraction) are maximised. Scratches and polishing streaks diminish these effects.
Since time immemorial the seeds of the carob tree were used to determine the weight of gemstones on the scales. These seeds have a very stable weight of 0.2 grams. In Greek this kind of seed is called Keration (in Arabic, ‘Kharrub’). The word carat is derived from this. Another weighing measurement used in the diamond trade is the grain that comes from the Latin word ‘granum’ meaning ‘grain’. The more or less standard weight of a grain of corn is 0.05 grams. In 1907, it was internationally established that 1 carat is equal to 0.2 grams, and equal to 4 grains. For diamonds, 1 carat is further subdivided in 100 points. The word carat is also used to indicate the gold content in gold.
Most diamonds contain flaws (inclusions) which came into being during the crystallisation process. A diamond free of inclusions is called internally flawless. Inclusions which can be observed with magnifying glass capable of ten times magnification decrease the value of the diamond. Professional organisations in the diamond trade have worked together internationally to draw up a table of clarity
The fact that not all world-famous diamonds are of the highest clarity is proven by the Hope and the Yellow Tiffany, which are VSI.
The Centenary Diamond is the largest diamond of an IF purity and a D-colour.