Diamond Grading Scales
Grading scales were developed by diamond specialists, as a means of evaluating the quality of a diamond. Diamonds symbolize rare beauty, perfection and purity. Their beauty is graced with toughness and timelessness. The diamonds owe their toughness to the fact that they are born in the fiery belly of the Earth and their optical clarity and transparency to a unique carbon crystal structure. Diamond has various applications like in diamond jewelry and industrial applications, where it is used as a cutting tool.
All diamonds are different though. Like people, a diamond inherits the nature of the environment, in which it has evolved. The diamonds vary in weight, color and their composition. The way a diamond is cut, that is given shape from its raw form, matters a lot. The optical properties of the diamond are dependent on its cutting. However, the color and the composition cannot be modified. There are imperfections in diamonds or blemishes, as they are called. That is why, cutting a diamond is an art. The beauty of a diamond and its inner potential should be brought out in the process, despite its inherent blemishes and limitations, without damaging it.
So it takes an artist to cut a diamond and a connoisseur to appreciate its beauty, truly. Over time a systematic method was developed to grade and evaluate the value of a diamond. The value of a diamond is decided by four parameters, called the 4 Cs, which are, 'Carat Weight', 'Clarity', 'Color' and 'Cut'. Every one of these parameters has an impact on the visual appearance of a diamond. Let us understand the logic behind the introduction of these parameters and the criteria for diamond evaluation.
Carat Weight Scale
Diamond is a gem stone. The standard adopted unit of weight for a diamond is 'Carat'. This is also known as 'Metric carat'. One carat is equal to 200 milligrams. So, a diamond weighing 5 Carat, is equal to 1 gram. One carat is divisible into 100 points of 2 milligram each.
The origin of the word carat, lies in the fact that earlier, the seeds of the Caribo plant called carat were used for weighing the diamonds. They were used because of their uniformity in mass and size. However the seeds are no longer used and now the carat word is only a namesake. The mass has been standardized by international agreement.
The largest known, cut diamond in the world currently, is the 'Golden Jubilee Diamond' which weighs 545.67 carats, that is about 109.13 g. It was discovered in South Africa, in 1985 and weighed 755.5 carats, i-e.151 grams, as an uncut gem.
Clarity Grading
A diamond is valued by how clear and homogeneous it is, as a crystal. There are two types of defects or imperfections that affect the diamond clarity. There are internal irregularities in crystal structure called 'Inclusions' and surface deformities called 'Blemishes'. A perfect diamond would be a homogeneous crystalline form of pure carbon and would be exactly clear. However, as I mentioned before, the diamonds do not form in an environment of pure carbon, there are other impurities around like nitrogen, boron and other elements. Also, the crystal structure may have deformities or misalignments. So, a diamond grading system for 'clarity' was developed. It gives a clarity grading of a diamond based on the exact number, location and overall effect of the inclusions and blemishes on the visual appearance of the diamond. The scale ranges through 5 phases, in increasing order of imperfections:
- Pure (with sub-gradation of flawless and internally flawless)
- VVS (very very small Inclusions with sub-gradation of VVS-1 and VVS-2)
- VS (very small inclusion with sub-gradation VS-1,VS-2)
- SI (Small Inclusions with sub-gradation SI-1,SI-2)
- I (Included with sub-gradation of I-1, I-2, I-3)
Color Grading
The next characteristic of a diamond noticed even before its clarity, is the color. Diamonds come in a varying range of colors, depending on the impurities they contain. Ideally, the best and most perfect diamond is colorless, like a drop of dew! However, that is not so and impurities only add to beauty. Impurities and imperfections make that diamond unique and beautiful in its own way!
So a color grading was developed using diamonds of specific colors, as standard reference stones. The two extremes of gradation, range from colorless called 'D' to multicolored which is classified as 'Z'. The graders use colorimeter that makes a computerized evaluation of the color. Following is the classification color scale in increasing order of color intensity and variability:
- Colorless (sub-categorized as D, E, F)
- Near Colorless (sub-categorized as G, H, I, J)
- Slightly Tinted (sub-categorized as K, L, M, N)
- Very light Yellow (sub-categorized as O, P ,Q)
- Light Yellow (sub-categorized as R, S, T )
- Yellow (sub-categorized as U, V, W)
- Light fancy (sub-categorized as X, Y, Z)
The cut grading scale evaluates the overall sparkle and brilliance of a diamond, after it has been cut and polished from its raw form. The cut grading of a diamond is a complex subject. A grader has to take into consideration, the facets, the facial angles and the overall geometry of the diamond. Without going into details, the classification scheme for cut scale, ranges from expertly cut (almost perfect shaped diamonds) to extremely irregular. The numerical gradation is as follows:
- Excellent (Ranging from 1+ to 1)
- Good (Ranging from 2 to 3)
- Average (Ranging from 3 to 4)
- Commercial (Ranging from 5 to 6)
- Irregular (Ranging from 7 to 8)
