While there are various considerations for the purpose of diamond grading, the gemologists mostly consider the main 4 Cs viz. carat (weight), color, cut and clarity. Therefore, the quality of diamonds depends on the clarity of diamonds. Quality is determined by the inclusions and surface defects. The “inclusions” refer to the visual appearance and presence of internal characteristics. Surface defect will be called blemishes.
Diamond with inclusions will contain crystals of some foreign material (which may include another diamond crystal also) or structural imperfections like small cracks, appearing whitish or cloudy. Relative clarity of diamonds will depend on the size, color, number, orientation, visibility and relative location or position, nature, colour or relief of the inclusions.
To ascertain the clarity, the stones will be magnified ten times and studied and a clarity grade will be assigned. However, many inclusions in the gem-quality diamonds do not have any bearing on the performance and structural integrity of the diamonds. When the presence of cloud is large, it will naturally affect the transmission and light scattering capabilities of diamonds. It is called “cut” of diamonds. In this category of diamond grading, there are five grades – Poor to Excellent.
Resistance to fracture of diamonds will be reduced by large cracks near or breaking the surface.
Diamonds having higher clarity grades will be highly valued. Those having highly rare flawless (FL) grade diamond will fetch the highest price. Other grades in this category will be I1, I2 and I3, I representing “imperfection”. Minor inclusions and blemishes stand as an evidence of natural origin; they are similar to fingerprints and serve as identifying marks.
Weight of the diamonds is expressed in terms of carat. One carat is 200 milligrams. To have fine-tuned measurement, a carat will be divided into one hundred points.
For colors, the diamond grading system will be D (most colorless) to Z (containing most color). Colorless diamonds will be rare.