Compared with colored gemstones, the prices for which are not regulated by any institutions, the value of a particular diamond can be estimated using the Rapaport Diamond Report. It is updated every week and publishes two types of prices: the first on the round cut stones, the second one, for fancy cuts. With other things being equal, the diamonds of the classical round form in fifty-seven faces, calculated and improved by the mathematician Marcel Tolkovski in 1919, are always more expensive — from the point of view of ideal proportions that optimize the play of light, there are no competitors. Stones of fancy forms — any that differ from the round in fifty-seven faces — lose from 20 to 40% in price depending on the size. For these cuts, symmetry is extremely important — otherwise passing light will be deflected incorrectly, creating ugly effects. Special attention should be paid to any old cuts, in which the culet, a small additional facet at the base of the pavilion resembling a spike, is often sawn down. To remove a well-viewed «window» in the center of such stones is possible only with the help of a re-cut; therefore they are available with a discount of 10-30%.
The Rapaport price list is based on the standards of assessment of the Gemological Institute of America (GIA) — the rest of the laboratories even certify the stones in accordance with the terminology of the GIA, but their reports often greatly embellish reality. Thus when the seller refers to the Rapaport price list, it is more desirable that he presents the GIA certificate. The Gemological Institute of America is the only one organization in the world that receives many grants from the state. Practically all laboratories are commercial, and they suffer very much from competition with their own kind. In order to increase customer loyalty, such organizations often overstate the real characteristics of the stones being evaluated, and much often not for a one scale mark. Very frequently, when you buy a diamond with no GIA certificate, you cannot save money, but overpay greatly.
When people say that prices for diamonds have come down, this is primarily indicative of an increase in the discount from the Rapoport price list for certain specific groups of stones. Also, you should always keep in mind the oversized stone: if we look at the table, the difference in price between stones of 2.00-2.99 carats and 3.00-3.99 carats is more than 40%, therefore the cost of a diamond weighing 2.8 carats will be calculated at a lower rate than the one at 3.00 carats, although the visual difference between them is almost unnoticeable. Therefore, stones that have a «bridging weight» (close to the next interval) can be up to 40% more expensive than the Rapaport rate. The situation is the same for diamonds weighing from 6.00 to 9.99 carats: until recently, the last gradation table was with diamonds weighing 5.00-5.99 carats, but then Rapoport added another one for stones from 10.00 to 10.99 carats. Consequently, if the diamond weight falls within the interval from 6.00 to 9.99 carats, its value is calculated at a rate of 5.00 to 5.99 carats plus a premium.
Small stones weighing up to 0.5 carats are usually sold either at the report’s price or with a discount till 15%, but the less ideal the mineral (because of a bad cut, fluorescence or black inclusions), the harder it is to sell (for example, in view of the outstanding size); and the more accommodating the seller. However, whatever one may say, there’s no such thing as a free lunch and a price reduction of more than 50% is usually offered by those whose stones are estimated to be less stringent than GIA standards. Therefore, in order to avoid overpayment, it is necessary to consider not discounts, but a concrete stone, resorting to the help of an experienced specialist.