Geological classification

When are diamonds not graded?

Expert evaluation is a procedure for evaluating a stone by comparing it with other diamonds according to certain criteria. The combination of such criteria constitutes an expert assessment system. Typically, an expert assessment of a stone is carried out according to four parameters (4 “Cs”): The first “C” is carat weight. At this stage, the exact weight of the stone is determined by weighing it on scales or calculating using formulas if the diamond is fixed in the product. The weight of a diamond is expressed in carats (1 ct = 0,2 grams). The second “C” is color. Completely colorless diamonds are quite rare, and almost all stones have shades of varying colors and intensities. The examiner’s job is to accurately determine the intensity and color of a diamond under standard lighting using color standards and assign a color grade. The third “C” is clarity (purity). At this stage, all internal imperfections (defects) of the stone are identified. The stone is graded based on its purity. The fourth “C” is cut (quality of cut). At this stage, characteristics of the diamond’s shape, cutting quality and finishing are given. Based on these parameters, one can judge how a given diamond stands out among other diamonds, on the basis of which it may be more expensive, or, conversely, cheaper. 1. EXPERT ASSESSMENT SYSTEMS In world practice, various diamond grading systems are used. The most common is the grading system developed by the Gemological Institute of America (GIA), and experts around the world are familiar with this system. Other well-known grading systems are the Belgian High Diamond Council (IDC or HRD), the CIBJO system, the Scandinavian Nomenclature (Scan DN), and sometimes older terms are used, especially to describe color. In Russia, the Russian assessment system is used (TU 117-4.2099-2002). This material focuses on the GIA and TU systems. Western systems, with the exception of rare cases, are easily translated into one another, while all of them cannot be unambiguously translated into the Russian system. 2. ESTIMATION OF THE MASS (WEIGHT) OF DIAMONDS The weight of an unmounted diamond is determined by weighing it on a carat scale. Weighing is carried out with an accuracy of at least the third decimal place, the mass is recorded to the second decimal place, the third digit is discarded if it is not equal to 9. Simultaneous weighing of a batch of diamonds is allowed. Small diamonds are often screened into size groups and are then sold by size. When combining and splitting lots of diamonds, there may be some change in the weight indicated in the documents. If a diamond is set in jewelry, its weight can only be accurately determined after setting. Therefore, it is strongly recommended to weigh the stones before setting them into products. The weight of mounted diamonds can be approximately calculated using formulas. For example, the formula for calculating the weight of a standard round cut diamond is: M=D 2 xHx0,0061 Where М – weight in carats, D – diameter, Н – height. In the case of a thick girdle, depending on its thickness, the coefficient of 0,0061 increases to 0,0067. The error in calculating mass using formulas is about 10% for properly cut diamonds and can be even greater for stones with distorted geometry, antique and unconventional cuts. When determining the weight of diamonds using formulas, you must indicate the fact that the weight was determined by calculation. 3. ASSESSMENT OF DIAMOND COLOR Diamonds that have no color and are completely colorless are especially valuable. Most gemstone diamonds have shades of varying intensities. Conventionally, all diamonds can be divided into two groups: a more numerous one with a yellow color or shade of varying intensity (the “Cape” series) and a group of fancy-colored diamonds. To accurately determine the color of cape diamonds, there are sets of color standards, for example, the most famous GIA standard scale (from D to Z). The color scale is divided into groups, it begins with completely colorless diamonds, then there are smooth transitions with increasing yellow color saturation and ends with the last group, which has a clear yellow color. According to the GIA system, it is customary to designate each color with a letter of the Latin alphabet from D – colorless to Z – yellow. Using the same scale, you can evaluate the color of stones of the brown series, and not the shade is taken into account, but only the color saturation of the stone. Yellow and brown stones with a color characteristic below Z are considered fancy. 3.1. GIA Color Grading One of the determining criteria for the value of a natural diamond is its purity, or transparency. Forming in the depths of the rock, adamant receives defects in the form of inclusions of foreign particles, or density features formed under the pressure of the mass of the formation. To determine the presence of inclusions, an expert uses a jewelry loupe or a special microscope, which allows one to see the nature of the inclusions, their shape, size and location. The size of the stone also has an impact on the clarity rating of the stones. Diamonds are divided into 2 groups:

  • less than 0,29 carats – without special equipment, inclusions with a grade of 5-6 will be visible on them;
  • for stones weighing 0,3 carats or more, defects can be seen with the naked eye at a purity of 6-7 and below 8-12.

The best are recognized as diamonds that include inclusions in the form of dots, in quantities from 1 to 4. Defects found on the surface practically do not reduce the value of the diamond, because during the cutting process they are eliminated, since during cutting it is not permissible for defects to come to the surface diamond Stones with defects inside can seriously affect the value of a diamond.

Diamond grading systems

There are several diamond grading systems. Four of those presented are recognized by the international community, and if you have a stone with a certificate from these organizations, then selling it will not be difficult. But, for example, the Israeli assessment system is not quoted on the world market and the expert’s conclusion will be questioned.

  • GIA (Gemological Institute of America) – recognized as a standard, with a high level of expertise;
  • Scan. DN (Scandinavian Nomenclature);
  • IDC (Supreme Diamond Council);
  • Russian TU system.

The evaluation criteria for American experts are the ability to determine the presence of inclusions with the naked eye or through a magnifying glass. The relief of inclusions, the nature of distribution in the thickness of the mineral, the size, and integrity of adamant are assessed. The Russian assessment system according to specifications examines transparency, the ability to see the edges of the pavilion through the platform and crown, the nature and nature of the existing inclusions, their appearance and shape.

Russian scale

In the Russian Federation, the Gemological Laboratory of Moscow State University is recognized as the leading expert in the industry. Our assessment system, unlike the Western one, is based not on comparison with a standard, but on a verbal description. Our system is considered more complex, since it takes into account not only the size and number of inclusions, but also the size of the stone, which directly affects their perception. When classifying, the clarity parameter is indicated after the slash and is supplemented by the cut characteristic. For example: 4/6 A. 4 – shade, 6 degree of transparency, A – quality of the cut. Stones without inclusions or flaws are classified as category 1.

  • Large stones weighing more than 0,3 carats and having 57 facets are differentiated into 12 categories.
  • Adamants with 17 facets are considered small; there are 6 categories for them.
  • Medium diamonds with 57 facets, weighing within 0,299 carats, are divided into 9 degrees of clarity.

Kr-57 up to 0,29 carats

Kr-57 from 0,3 carats

In accordance with the Russian grading system, flaws that can be distinguished with the naked eye are visible in stones of the 0,299th purity category for medium-sized stones up to 6 carats, and for large ones – in the 7th purity category.

Gemological Institute of America (GIA) assessment

When assessing the degree of transparency of adamant, GIA experts rely on a comparative analysis of the sample with the standard. In this case, only defects that can be seen at 10x magnification are taken into account. A certificate issued by the Gemological Institute of America is considered the highest guarantee of the quality of a diamond and jewelry. You can sell such a stone anywhere in the world, its characteristics will not be questioned. Unlike the Russian technical specifications, differentiation into categories based on visual characteristics and their abbreviations is used for classification.

The stone is free of external and internal defects. An impeccable example. Or minor defects on the surface will be removed by grinding.

The presence of a microdefect in the form of 1-2 inconspicuous dots or a single stripe. They can be easily eliminated by peeling the stone at the beginning of cutting. The inclusions are visible only through the pavilion and will be removed by sanding.

Very Very Small Inclusions

Microdefects in the form of 1-2 stripes, 1-4 light defects or 1-2 dark defects are acceptable. It is difficult to see through the platform.

1 microcrack, 3 light blotches or 1 stripe is acceptable. Cloudy and cirrus inclusions are difficult to see under a magnifying glass.

Very Small Inclusions

1-6 mini-defects, stripes, light or dark inclusions, 1-3 dark small inclusions. Clouds or cirrus may be seen.

1 dark volumetric mini-inclusion, 1-5 mini-inclusions of a dark shade, 1-8 scattered mini-defects (stripes, cirrus, clouds, cracks). Small inclusions can be seen at 1x magnification.

Up to 2 small inclusions or a couple of small cracks can be seen under a magnifying glass.

A professional can distinguish up to 8 small inclusions of various shades without a magnifying glass, or with one.

The stone is imperfect. Many microcracks, large inclusions of various shades, visible to the naked eye. Diamond is not suitable for making jewelry or investing.


Principles of color evaluation, color or purity: what to choose

It is noteworthy that a color rating system has also been developed for diamonds. For colorless stones, the complete absence of shades is considered ideal. Blue or greenish are allowed, but a gradation from yellow to brown gradually reduces the cost of the stone. The cheapest stones will be brown tones. Here the Russian scale also relies on descriptive characteristics, and we have a separate scale for assessing yellow and brown stones. GIA experts base their work on comparison with a reference sample.

It is also important that American gemologists have developed a separate grading scale for fancy colored diamonds, which is not provided for in the Russian system.

  • Champagne;
  • Yellow;
  • White;
  • Pink champagne;
  • Brown-pink;
  • Pink;
  • Purple pink.

GIA chromaticity implies differentiation into 7 colors, where the intensity of each is measured on a scale of 1-7. A unit is assigned to the most saturated color specimen.

Diamond Color Chart

Russian differentiation system

Stones 0,29 carats and less

Stones 0,3 carats and above

The purest stone is a bluish-white, barely visible shade. When visually inspected across the platform, it appears colorless.

Upon expert evaluation, the stone is defined as bluish-gray.

Transparent white with a bluish tint that only an expert can see

To the uninitiated, the stone appears colorless. The expert is able to distinguish a bluish tint of the watery-colorless crystal; there is a hint of yellowness.

A yellowish tint or grayish-white tint can be seen when compared with the standard. A layman may not be able to distinguish yellowness. Such stones are the most common.

Grayish-white or white with slightly pronounced yellowness. You can consider it when compared with a colorless stone.

Even a non-specialist can distinguish shades of gray, green, lemon or yellow.

A yellow tint of moderate severity, visible to the naked eye of a layman.

Yellow and yellow-brown shades.

The difference in shades significantly affects the cost of the stone, although it may not be visually visible. That is why the mass consumer is recommended to pay attention to stones with average performance. They will be affordable, but people around you without special equipment or comparison using a reference sample will not be able to determine the real quality of the diamond in the jewelry. Through cutting, the color and clarity of a diamond can be greatly enhanced, or the focus can be on a particular characteristic, allowing for significant variability in selection.

The cost of a diamond depending on its clarity

How much does the cost of a diamond change depending on the concentration of foreign inclusions? When assessing the cost of a stone, a certain set of criteria is taken into account, called 4C:

  • purity – clarity;
  • color – color;
  • cut – cut;
  • weight, or carat – caratweight.

The most expensive stone will be the one with the highest ratings on all four of these scales. At the same time, it is tedious to take into account that there are several assessment systems; depending on the country, expert verdicts may differ.

The more transparent the stone, the higher the cost. Absolutely colorless diamonds have the highest value. However, there are exceptions for fantasy diamonds, where the value is influenced by the uniqueness and intensity of the color.

General grading rules according to Tavernier’s rule are suitable for stones weighing less than 5 carats. In this case, to determine the total cost, the base cost of a 1-carat diamond is multiplied by the square of the stone’s mass expressed in carats. Large stones heavier than 5 carats are rare, so their evaluation takes into account individual characteristics. Very rare diamond samples receive personal names and are considered works of art.

Optimal balance of purity and color

Depending on the purpose of purchasing a diamond, the buyer should take a closer look at the clarity and shade of the stone. The purchase can be a collector’s item, for investment purposes, or simply as a decoration for yourself or as a gift to a loved one.

Flawless stones, transparent like a child’s tear, are a unique phenomenon. The scale rating will be 1/1. Their cost can reach several millions. Diamonds with 2/2 values ​​are valued slightly lower, but only an expert with special equipment can tell the difference.

Let’s say you’re interested in investing. In this case, it is recommended to choose stones with a purity in the range of 3-6. Even if in the future you want to sell stones, their value on the market fluctuates little, which allows you to save savings from inflation.

The most common case is the purchase of diamond jewelry. It is important here that the stone matches the setting, looks good and is affordable. The optimal solution would be stones with a rating of 6/6. Their distinctive feature is that defects are invisible to the naked eye. Unless you are planning to meet with an expert collector, absolute perfection is not required.

Choose a higher quality stone shade if you are planning a frame made of white gold, platinum or silver. If the stone has a tint, a light metal will make it more noticeable. But when setting them in yellow metal, you need to pay attention to the cleanliness of the stone – since against the background of the setting, inclusions will be more noticeable and the stone will look dirty.

What to consider when buying diamonds

A prerequisite for purchasing precious stones must be a licensed salon. If you decide to purchase jewelry from a private collection, be sure to enlist the support of a specialist and, if possible, obtain a conclusion from a gemological laboratory. The jewelry must be accompanied by a document certifying the authenticity of the stones. If these are diamonds weighing less than 0,5 carats, then the manufacturer attaches a passport tag indicating the number of stones, weight, color, type of cut and number of facets, and quality. You can decipher the abbreviations using a special table, which you can ask the seller.

For precious stones weighing more than 0,5 carats, the law requires a certificate or passport indicating the conclusion of the gemological examination. In addition to the previously indicated characteristics, the certificate includes data on inclusions (a map indicating the location), as well as metrics – length, width, height and diameter of the diamond.

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