The 4C grading standard is used for both cultured and natural diamonds. In the 1940s, the Gemological Institute of America (GIA) initiated the "4C from the perspective of color, the standard and international diamond grading system, from the four dimensions of Colour, Clarity, Cut, and Carat diamond certification.
Diamond color is divided into 5 grades, including Colorless(Colorless, containing DEF color), Near-Colorless(Near Colorless, containing GHIJ color), Faint(pale yellow, containing DEF color), and Faint(Faint yellow, containing GHIJ color). Including KLM), Very Light (including N-R), and Light (including S-Z), the closer the diamond is to colorless, the higher its value (except for color diamond);
There are six levels of clearness and they include Flawless, IF, Very Very Slightly Included (VVS, Slightly Included (VVS1~VVS2), Very Slightly Included (VS, minor flaw, including VS1~VS2), Slightly Included (SI, minor flaw SI1~SI2), Included (I, including I1~I3); Slightly Included (VS1~VS2), Slightly Included (SI, minor flaw SI1~SI2), Slightly Included (I, including I1~I3).
There are five grades of cutting, including Excellent, Very good, Good, Fair, and Poor.
The International Gemological Institute (IGI) began to provide diamond cultivation testing and certification services every year in 2005. In 2021, IGI became the first to obtain ISO diamond certification. GIA synthetic diamond was launched in 2007 and the identification certificate was issued in July 2019. The laboratory diamond cultivation certificate was available from January 2021. In March, China National Jewelry and Jade Quality Supervision and Inspection Center (NGTC) launched a special testing certificate for the cultivation of diamonds.