The same four basic parameters that govern the grading of all gemstones are used to grade blue diamonds–the four Cs of Connoisseurship:
color,
clarity, cut and
carat weight. Color is considered the most important criterion for grading a blue diamond and determining its value. There is no known blue diamond with a completely flawless (F) clarity grading, although several are known which are graded Internally Flawless (IF). One of the earliest mentioned blue diamonds is the
Hope Diamond, a 45.52-carat fancy dark grayish-blue which is believed to have been discovered in India but whose first recorded presence was in 1666 by French gem merchant
Jean-Baptiste Tavernier, after whom it was called the
Tavernier Blue. Its last owner was famed jeweler
Harry Winston before he donated it to the
Smithsonian National Museum of Natural History in Washington, D.C. Colorless (“White”) diamonds have remained the most popular type of diamond through the millennia, but the existence of this blue diamond so long ago affirms the reality of the demand for fancy color diamonds over the years.
Color In gemology, color is divided into three components:
hue,
saturation and
tone. Blue diamonds occur in hues ranging from green-blue to gray-blue, with the primary hue necessarily being blue. Green and gray are the normal secondary hues that can be found in blue diamonds. Blue diamonds are considered most beautiful and valuable when no secondary color is present but are pure blue. However, a pure blue diamond of light color may be considered less valuable than a green-blue or gray-blue diamond whose color is more vivid. The characteristic of color is very complex in blue diamonds for this reason. Most pure blue diamonds are
Type IIb, meaning they contain either very few or a complete lack of nitrogen impurities.
Type Ia Blue stones contain a secondary hue and get their color from the presence of hydrogen.
Clarity As with all diamonds, the
loupe standard is used to grade clarity. This means that the inclusions are judged based on the appearance of the diamond under 10x magnification, and not how it would appear to the naked eye.
Treatments Blue diamonds are only considered rare and valuable if they are natural. The definition of a natural blue diamond is a blue diamond that was mined with its blue color already present. Since the 1950s, many methods have been developed to change a diamond’s appearance, including adding color to a colorless stone. These are considered
enhanced diamonds and do not have a natural blue diamond value or resale value. Enhanced blue diamonds are not bought with the intention of investment or eventual resale. Synthetic blue diamonds have also been made, using the
HPHT method. ==Mines==