The Nan Yang Gemological Institute, NGI, released the Diamond Identification and Grading Chart in 2006. This chart provides a comprehensive overview of diamond identification and grading. It includes a classification of diamond types, namely Ia, Ib, IIa, and IIb. The chart adopts the widely recognized 4C grading methodology, which assesses diamonds based on their carat weight, color, clarity, and cut. Additionally, the chart highlights various treatments applied to diamonds, as well as the synthetic (lab-grown) diamonds and diamond simulants commonly seen in the industry. It also covers the gemological instruments used to detect these treatments and imitations. Lastly, the chart incorporates weight estimation formulas for diamonds with common cuts.
You may collect a copy of the Chart free of charge at the NGI office.
NGI is in the process of updating the chart.
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