Diamonds are graded on the 4 Cs: color, carat, clarity, and cut. Colorless diamonds are the most desirable and highly rated.
Diamond, a transparent crystal formed from tetrahedral bonding between carbon atoms, is the hardest natural substance on Earth. Its name originates from the ancient Greek script - adamas.
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Gemstones, primarily used for adornment, are highly valued for their exceptional physical feature of dispersion, which creates a spectrum of colors from white light.
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The four major parameters, also known as the 4 Cs, carry the paramount importance while evaluating the quality and price.
The 4 Cs are Color, Carat, Clarity and Cut. So, it is important to understand the grading and phenomena associated with it, when planning to purchase it. By understanding these parameters, you can decide which graded diamond to go for.
Perfect diamonds are completely transparent with no hue, rare and graded higher due to colorlessness, lightness, and chroma.
Color is typically influenced by structural defects in the crystal lattice, with chemical impurities also affecting deviation from perfect white.
Hue and saturation of color decide its value. When more or less yellow hue is present, it is regarded as less expensive, while pink or blue hue can boost its price. One of its best examples lies in Hope Diamond which is dramatically precious. In general, the ones used in gemology are basically transparent with a little tint.
They are also known as white diamonds. Nitrogen is the most common impurity found. Due to its presence in the structural bonding, replacing carbon atoms leads to yellowish, brownish tint.
The grading process, evolving since ancient times, gained standardization in the 20th century. Three main organizations oversee this global standardization.
Color Gradation
Mainly three organizations are responsible for this standardization of gradation system.
1. American Gem Society (AGS) - Although a new platform for gradation in comparison with GIA, it is renowned for a grading system based on numbers.
2. American Gem Society (AGS) - Although a new platform for gradation in comparison with GIA, it is renowned for a grading system based on numbers.
3. Diamond High Council (HRD) - Based in Antwerp, it is the authority to issue official certification.
20th century has seen emergence of a color gradation system ranging from D to Z, where D denotes for colorless and Z denotes for bright yellow coloration. This system has universal appeal unlike other systems present earlier. It assesses the diamond in comparison with the benchmark set in the presence of standardized lighting parameters.
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Gemstones graded D-F: colorless, G-J: near-colorless, K-M: slightly colored, N-Z: light yellow or brown. Master sets are Cubic Zirconia.
Classification of Diamond
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Diamonds come in various colors like yellow, pink, red, blue, green, brown, and others due to impurities and structural shifting. Intense saturation leads to fancy colored diamonds.
Though there are rating systems for such diamonds, because of their vast variation, no common grading system exists. Basically, they are classified into two types based on the impurity involved.
The main impurity, nitrogen, at around 0.1%, is classified into IaA and IaB, leading to yellow to brown tint.
1. Type I Diamond
IaA and IaB are collectively known as cape series. When nitrogen is not present in a pair but scattered around the structure, the type is known as Ib, which gives intense yellow colorization to the diamond. They are characterized by visible absorption spectrum and have a typical fluorescence.
Fewer nitrogen impurities create colors like pink, brown, and red due to rare plastic deformation. Type IIb diamonds range from blue to gray due to hydrogen or boron within the crystal matrix.
2. Type II Diamond
Factors Affecting Color
Parameters like fluorescence, enhancement techniques like HPHT and irradiation, affect the color of a diamond.
Fluorescence
It creates a major coloring effect, positive or negative, in presence of light. Virtually all exhibit this property in presence of X-rays or UV rays. This helps in identifying diamonds. Fluorescence if strong, may alter the perceived color of the diamond positively or negatively. Hence, the gemstone that has no effect with fluorescence is rated higher.
HPHT (High Pressure/High Temperature)
It is a color enhancing treatment developed primarily by GE. An annealing process which involves high pressure and temperature, can change low color or fancy brown color gems to colorless gems. The change is permanent and can yield less expensive gems.
Irradiation
This process is carried out with the help of linear accelerator in combination with heating to produce fancy colored diamonds.
While making a purchase, you should always look for the graded color parameters. Colorless or near colorless ones are most expensive while others are less expensive.