As a buyer, you need to know how the price of a diamond is determined. To begin with, you must ensure that the diamond is natural, as only price list data is applicable to natural diamonds. There are also "synthetic" diamonds on the market, which are not subject to the same regulations as natural diamonds.
The weight, color, clarity, and cut of a diamond all play a role in determining its value, as do the other "4'C" characteristics - shape, appearance, and quality. Besides these, the presence and intensity of luminescence, the accompanying gemological reports to the stone, the type of market and location of purchase and sale, and additional terms of the transaction are all important factors.
"Diamond" refers only to faceted natural diamond that can be refined in color and/or purity.
Each week on Friday, Rapaport publishes its Rapaport Price List, which is the primary market indicator for determining the value of loose diamonds.
Price lists from Rapaport are broken down into two categories: "Round" (57 brilliant-cut diamonds) and "Pear" (all other fancy-cut diamonds). Find out more about the various ways diamonds are cut by checking out this article. Additionally, based on data published in the journal "Rapaport," each form's weight range is assigned a unique conversion factor.
GIA gemological reports certifying the declared quality characteristics of "A3" cut quality loose diamonds with the Rapaport classification (Very Good according to the ISO and GIA classification) reflect high retail supply prices in the New York region. It is the price list itself that serves as an indicator of the market's average supply prices. Rapaport's price list includes premiums and discounts based on a variety of factors, including the quality of the cut, the condition of the stones, the completeness of the paperwork, the location of the transaction, and more. Coefficients with a higher or lower mark-up discount value can be applied to certain rocks, but the standard range is between +15 and -35 percent mark-up discount
Let's take a look at how to use the Rapaport price list in greater detail. Diamonds' color characteristics are shown in the left columns, and the weights and purity characteristics are shown in the upper two rows, respectively. In addition, the extra weight correction factor is provided for stones located in the higher mass range. The final price per carat is given in hundreds of dollars when the rows and columns of the table intersect (Fig. 1).
Main table discounts for luminescence and premiums for diamond weight (compared to 5.00-5.99 carats) in the range of 6.00 to 10.00 carats are also included in the tables. In addition to the price lists, the Rapaport online trading network provides a discount-allowances reference table for round diamonds that reflects the actual market value (Fig. 2).
The RapNet trading network is a better source of information for determining the value of a diamond. Using this service, you'll be able to see current offers and previous transactions, as well as learn about additional terms for selling a stone (the presence of a gemological report containing assessments of characteristics according to the international standard, cut parameters, luminescence, etc.).
For example, there is a 0.38 carat "Round Brilliant cut" diamond with a GIA gemological certificate. The color is "H," the purity is "VS2," the cut is "Very Good," and the stone emits a bright blue luminescence, making it ideal for jewelry.
Step 1.  We use the Rapaport price list for the current time period to calculate the basic cost indicator:
Fig 1. Finding a basic indicator of the cost of a diamond with the given characteristics according to the price list of Rapaport - 1700 $ / ct.
Step 2.  Correction of the basic indicator of the value of a diamond in accordance with the adjustment for weight and quality of cut (+ 10% - + 20%), select + 15%.
Fig. 2. Determination of the discount on the luminescence of a diamond with specified characteristics according to the discount table Rapaport - (-2% - -3%), we accept -2.5%.
Step 3.  Using the application of discounts on the luminescence of diamonds for the current period of time, we determine the discount on the luminescence of our diamond:
Step 4.  Using the RapNet application for the current period of time, we determine the regular trading discount for our diamond:
Step 5.  Determining the average market value of a diamond with specified characteristics on the basis of a basic cost indicator in accordance with the Rapaport price list:
(Baseline + adjustment factor - luminescence discount - regular trading discount) x Carat weight = (1700+ 15% - 2.5% - 28%) x 0.38% = $ 521.52 per stone.
Because of this, it's important to keep in mind that the average market value may differ significantly from the real diamond offer prices.
Besides Rapoport, there are other professional publications that offer a review of diamond prices, each with a different audience in mind. Because it is intended for professional appraisers in the United States, the Gem Certification & Assurance Lab's The Palmieri's Market Monitor accurately reflects the state of insurance valuation in the country.
Jewelry and diamonds are the primary focus of The Gem Guide's editorial staff (in the US region). Additionally, this publication provides a wider range of basic shapes and cuts of the diamonds, and also the prices of diamonds of extraordinary and fancy colors. However, this publication is only released four times a year, and the sample size is significantly smaller than that of the Rapaport network.
For example, there are other retail sales market reviews, but the Rapaport information network is the most authoritative reference and information source.