Diamond Color

Diamond, a transparent crystal made up of tetrahedral bonding between carbon atoms is the hardest natural substance present on the earth. The name originates from ancient Greek script- adamas. Although diamonds have many uses, its most noticeable use is as gems stones for adornment. Its exceptional physical feature of high dispersion index makes it one of the most valuable gem stone. Dispersion of white light in to array of spectral colors is the premier gemological feature of diamonds.

The four major parameters, also known as the 4 C’s, carry the paramount importance while evaluating the quality and price of diamonds. This 4 C’s are Color, Carat, Clarity and Cut. So, it is of utmost importance to understand these grading and phenomena associated with them if you are planning to purchase a diamond. By understanding these parameters, you can decide which graded diamond to go for. Let us look at color to understand its grading better.

Although, a structurally perfect and chemically pure diamond can be defined as the one with complete transparent appearance with no hue or color, in reality no such gem size diamond can be found perfect. The lack of color contributes towards the higher grading of diamond. Hue is one of the main attribute of perceived color besides lightness and chroma. The color of a diamond is generally affected by few structural defects in its crystal lattice. Chemical impurities also contribute towards deviation of color from perfect white.

Hue and saturation of color decide the value of diamond. When more or less yellow hue is present, the diamond is regarded as less expensive gem stone, while pink or blue hue can boost its price. One of its best examples lies in Hope Of Diamond which is dramatically precious. In general, the diamonds used in gemology are basically transparent with a little tint. They are also known as white diamonds. Nitrogen is the most common impurity found in white diamonds. Due to its presence in the structural bonding, replacing carbon atoms leads to its yellowish, brownish tint.

Color Gradation
Although the gradation process of diamonds exists from ancient ages, 20th century has seen more standardization for gradation of diamonds based on their color that are accepted world wide. Mainly three organizations are responsible for this standardization of gradation system.
1. Gemological Institute of America (GIA) - the first laboratory to address the aspects of grading and holds high regard for its consistent and strict norms of grading.
2. American Gemological 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 on diamond gemology.

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 asses the diamond in comparison with the bench mark set of diamonds in the presence of standardized lighting parameters. Diamonds graded between D-F are considered "colorless", between G-J is considered "near-colorless", K-M are "slightly colored". N-Y usually appears light yellow or brown. The master sets used are precisely crafted and known as Cubic Zirconia.

Classification
Diamonds vary in colors like yellow, pink, red, blue, green, brown and many other tints due to variety of impurities and structural shifting. When ever there is unusual intense saturation of colors then the diamond is termed as fancy colored diamond. Though there are rating systems for such diamonds, because of their vast variation no common grading system exists. Basically, diamonds are classified into two types based on the impurity involved.
1. Type I Diamond - the main impurity is of nitrogen at a concentration around 0.1%. They are further classified into IaA where structure of diamond is characterized by presence of nitrogen pair bonded with carbon atoms and no effect on color. IaB represents those diamonds which are characterized by even number of nitrogen atoms. They lead to produce yellow to brown tint. IaA and IaB are collectively known as cape series. When nitrogen is not present in 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.
2. Type II Diamond - these diamonds carry less nitrogen impurities. Type IIa diamond with colors like pink, brown and red, their formation is a result of plastic deformation and is very rare. In Type IIb color varies from blue to grey due to the presence of hydrogen or boron scattered within a matrix of crystal.

Factors affecting color
Parameters like fluorescence, enhancement techniques like HPHT and irradiation affect the color of diamond.
1. Fluorescence: this creates a major coloring effect positive or negative in presence of light. Virtually all diamonds fluoresce in the presence of X-rays or UV rays. This characteristic also helps in identification of diamonds. Fluorescence if strong may alter the perceived color of the given diamond positively or negatively. Hence the diamond which has no effect with fluorescence is rated higher.
2. HPHT (High Pressure/High Temperature) - This 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 to colorless gems. The change is permanent and can yield less expensive gems.
3. Irradiation- This process is carried out with the help of linear accelerator in combination with heating to produce fancy colored diamonds.

While purchasing a diamond, you should always look for its graded color parameters. Colorless or near colorless diamonds are most expensive while others are less expensive.