«Eg-labs» laboratory provides gemological evaluation of diamonds on the basis of 4C's of diamond quality: carat, color, clarity, cut, which is the basis of all international gemological laboratories.
Is a unit of mass and is used for measuring diamonds. The origin of this name dates back to a wood named Carato. Its seeds in ancient times were used as the standard mass (1 carat = 0.2 gram). Depending on the weight of the diamond they are subdivided into small (up to 0.29 carat), medium (from 0.30 to 0.99 carat), large (from 1.00 carat and more).
The weight of a diamond is directly related to its price and is an important pricing factor. The basic principle for the valuation of diamonds is "Tavernier rule". According to this rule the value of the gem is equal to multiplication crystal`s square of the mass in carats on a base price per carat. For example, a diamond weighting 2 carat is 3 times more expensive than a stone with the weight of 1 carat and a 3 carat diamondis 10 times more expensive than a diamond weighting 1 carat.
Color of the diamond depends on an indicator of scale representing a color transition from colorless diamonds to yellow, each color corresponds to a letter of the Latin alphabet from D (colorless) to Z (yellow).
Gemological assessment of diamond`s color is produced while viewing the stone from the pavilion under a lamp with cold light on a specially folded sheet of paper (the boat). Diamonds with colors D-G are characterized by the absence of yellow tint when viewing from the table of the diamond. Stones with lower colors, from H to I, have a yellow tint from both the pavilion and the table. Diamonds below K color have a clear yellow tint and can vary by its intensity.
Assessment of the clarity of a diamond is based on the presents of defects contained in stone which can be detected while viewing it through 10x times gemological magnifying glass.
In line with this, there are five quality grades of diamonds:
1) INTERNALLY FLAWLESS (IF) – defects in the diamond are not visible neither from the table nor from the side of the pavilion. Such stones are additionally checked under the microscope.
2) VERY VERY SLIGHTLY INCLUDED (VVS) – the defects are very small and visible only through the pavilion. They are subdivided into two groups - VVS1 and VVS2. The location of defects in the diamonds of these subgroups is limited to the peripheral area of the stone.
3) VERY SLIGHTLY INCLUDED (VS) – minor defects, which can be in any area, including under the table, and viewed from the side of the table and pavilion. Depending on the number and size of defects, the group is subdivided into subgroups VS1 and VS2.
4) SLIGHTLY INCLUDED (SI) - obvious internal defects in a diamond. There are subgroups SI1, SI2, SI3. Defects in the stones of these subgroups are quite large and numerous. This can be cracks, clouds, graphite inclusions and small chips.
5) INCLUDED (I) – a variety of defects in different parts of the stone, visible without a gemological magnifying glass.Depending on the degree of imperfection the stones they can be subdivided into a subgroup of I1, I2, I3. Defects in these diamonds are represented by numerous cracks, including defects on the surface, large and dark graphite inclusions, twin seams, clouds, chips. The defectiveness of the diamonds in these groups usually exceeds 50% of the volume of the stone.
Cut of the stone directly affects the optical properties of diamond: brilliance, sparkle, scintillation and dispersion.Therefore, the value of a diamond depends on how well its cut is.When the diamond is properly cut,the light passes throughthe table or can be facedto the crown,reflected from the pavilion and back, experiencingthe smallest dispersion.If the cut is unsuccessful, then the light passing through the area, reaches the pavilion facets and passes through one of themor leaves through the opposite bottom face of the diamond, with having no time to reflect. The less refracted light returned to the observer is, the lower the optical properties of diamond is.
Depending on the light altering properties of the quality of a diamond cut is divided into: excellent, very good, good, poor, fair.