1. Grading based on crystal morphology and location of flaws
Generally divided into the positive crystal, distorted crystal, triangular flake, contact twin crystal, and aggregate form. Among them, the business is divided into:
Stones: Refers to high-quality diamonds over 1 กะรัต.
Fancy Colours: The color of these diamonds does not include colorless with blue or yellow tints, but refers to bright and bright Fancy Colours such as blue, green, canary yellow, brown and rose.
Closed stones: Single crystal with a nice shape for sawing and polishing.
Spotted stones: Single crystal, nice shape, not very pure (heavy blemishes), but they can be removed when cutting.
Naats: Distortion of the crystal, should be cleaved or cut directly.
Irregular stones: have an irregular octahedral or dodecahedral shape and can be cut directly.
Cleavable stones: Diamonds that should be cleaved.
Coated stones: These diamonds require some thought, as they are surrounded by a rough coat. Unveiled they may still be dim, but they may also be a gem.
Frosted stones: Similar to Coated stones, except that the coat is now translucent.
Milky stones: As the name suggests, these stones have a milky white appearance.
Blocks: have a special shape and it is difficult to see their crystal orientation.
Plats: These diamonds are usually twin and are often used for rose cuts.
Sands: Refers to very small diamonds (less than 0.10 กะรัต), used for type 8/8 cuts.
Commons goods: The quality of these diamonds has been mediocre and is on the limit of gem-quality diamonds.
Rejections stones: Diamonds of unqualified quality for the jewelry industry should be excluded.
2. Classification of crystal surface features
Generally, according to the depth and size of the triangular pits on the crystal surface and whether there may be stress cracks, it is divided into excellent, ดี, medium, and poor.
3. Crystal color grading
Usually, the colors are colorless, milky white, light green, yellow, สีเหลืองอ่อน, black, brown, ฯลฯ. Among them, light green diamonds are the most gambled. Generally, high-color bare stones can appear. gambling. Among them, yellow and brown diamonds are divided into yellow, สีเหลืองอ่อน, white and excellent white.
4. Grading of crystal size
Generally divided into 0.5ct, 1กะรัต, 2กะรัต, etc., it is divided into small stone, middle stone, large stone, and extra large stone.
5. Grading of crystal clarity
Generally, it is divided into defect grade, heavy defect grade, and clean grade with 10 times magnifying glass under special lamps.