2 Diamond Fraction Carat Weight: The weight of a diamond is calculated in carats, 1 carat equals 0.2g, 1 carat can be divided into100th, and a 0.5-carat diamond is often called 50 cents. Generally, the evaluation of carat weight of diamonds is divided into five unit price grades, such as: 5-9, 10- 14, 15- 19. However, diamonds above 1ct are called big diamonds, and diamonds weighing tens of carats are quite rare and valuable. So the unit price of diamonds is directly proportional to the weight of diamonds.
3 clarity classification
(1) Internal features, also called inclusions or inclusions, refer to various defects contained in diamonds. External characteristics are also called external defects: it refers to the defects on the surface of the finished diamond.
② Definition of cleanliness grade: flawless (FL), immanent (IF), extremely flawless (VVS)VVS 1, VVS2, slightly flawless (VS)VS 1, VS2, small flawless (SI)SI 1, SI2, heavy flawless (V).
Four mineral credits for diamonds
Type I: Diamond contains impurity "N" (nitrogen) and cannot transmit short-wave ultraviolet light with wavelength of 250nm. Type I diamonds account for more than 98% of all diamonds and are divided into two subtypes: Ia and Ib.
Type Ia: it contains "n" impurity, about 0. 1%, and there is an aggregate "N3" of "n" in the crystal lattice, which leads to the absorption of 4 15nm, thus causing yellow, which is called Cape series or yellow series. Most type Ia diamonds have different fluorescence intensities under ultraviolet light, usually blue and white.
Type Ib: It contains "N" impurity, up to 0.20%, and "N" replaces "C" atoms in diamond lattice in the form of isolated atoms. The spectral absorption of Ib diamond is stronger than that of Ia. It absorbs ultraviolet rays from 500nm and can form yellow colored diamonds, which are called canary series. Type Ib accounts for about 0. 1% of all type I diamonds, but almost all synthetic diamonds are type Ib.
Type Ⅱ: Diamond contains almost no "N", and its spectrum can transmit short-wave ultraviolet light below 220nm. Type Ⅱ is divided into two subtypes, type Ⅱ A and type Ⅱ B. ..
IIA: Almost all big diamonds belong to IIA type. The color is colorless or slightly gray or brown, accounting for about 2% of all diamonds.
Ⅱ B: "B" containing trace boron is blue, with semiconductor characteristics, which is very rare. The star of the sea in the Titanic movie is also called the star of hope. When it was discovered in India, the owner wanted to give it to the Queen of England in order to get a job. Unfortunately, the person who owned it died. At the same time, it is also called "disaster star" (meaning that whoever owns it will have disaster).
5 diamond classification (4C)
The better the cutting, the brighter the standard round drill, and the higher the value. Every gem-grade diamond is very beautiful and unique. Because they are natural, it is impossible to find two identical diamonds. Craftsmen always use diamond materials as much as possible, so a slight difference can determine their different values. The evaluation and classification of diamonds begin with color, purity, cut and carat weight. Because the first letter of their four English words is "C", diamond grading is also called diamond 4C grading.
6 color grading
GIA's color scale is expressed by English letters, with the highest color scale starting from D and the lowest color scale being Z. * * * has 23 color scales.
Conditions for color grading
(1), yellow series or diamonds with other shades, depending on the shade.
(2) The basis of color classification is the comparison among colorimetric stones, samples and colorimetric stones to determine the color grade.
(3) Classification must be carried out under a suitable light source.
(4) Classification must be carried out in a neutral color environment.