The color undertone of these diamonds therefore can only be judged by visual inspection. Lab reports from the Gemological Institute of America (GIA) Ref 1-2 and the American Gem Society (AGS) do not rate Brown or Gray undertones of a diamond that are J color and above. Left typical yellow undertone, Right with a gray undertone.
1-1- Two GIA Certified Identical "I" Color Diamonds.
Traditionally, diamonds having an undertone other than yellow are considered undesirable by jewelers and are typically traded at a discount. Milky diamonds are typically found with stones that have high levels of fluorescence. The first two terms of Brownish and Greenish are used to denote the color undertone while the term "milky" is used to define diamonds that have a slightly dull appearance without the superb luster and translucency that diamonds are known for. In the "trade", the terminology “No BGM” (No Brown, Green or Milky) has become a commonly used term by traders to confirm that a diamond is not Brownish, Greenish or has a Milky luster. A greenish undertone usually denotes diamonds sourced from the African country of Zimbabwe which are known for having this characteristic. A gray undertone can be more clearly thought of as a tonal characteristic rather than saturation which slightly darkens the appearance of a diamond. Although more rare, greenish and grayish undertones also exist (Ref. Other hues or undertones besides yellow can also be found, the second most common of which is brown. The most common and expected undertone hue in diamonds is yellow which is never noted in a lab report. Within these progressively higher color saturations in lower colors, you can have different hues of color. If the grade D represents the absence of any color in a diamond and Z is the most colored, the saturation of color increases progressively as you go down the color scale. Color Undertones DefinedĬolor undertones can be explained in layman's terms by thinking of them as being the hue and the combination of saturation and tone from the color spectrum. In reality, there are many color undertones other than yellow which can lead to drastically different appearing diamonds even within the same color grade. The common misconception is that with progressively lower colors, diamonds move in a straight line from white through an increasing pure yellow. Many consumers today are unaware of the impact that a “color undertone” has on the appearance and ultimately the value of a loose diamond.
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