How Colored Diamonds Get Their Hue

White diamonds are the most common hue, falling into the largest color spectrum on the Diamond Grading Scale, which begins with “D” color, meaning totally colorless, and ending with “Z” color, which is pale yellow or brown.

The variable in this spectrum is the element nitrogen – a D color diamond has no nitrogen (or only a microscopic amount) nor any other element present. The larger the amount of nitrogen present, the more the color increases, thus moving the diamond along the color spectrum.

The vast majority of white diamonds mined today have a large content of nitrogen, which classifies them towards the lower end of the color scale. Diamonds that fall within the D–F color range are rare, and therefore will typically command a higher price than those towards the end of the spectrum.

Yellow diamonds owe their hue to the presence of nitrogen impurities within their carbon crystal structure. These nitrogen atoms alter the way the diamond interacts with light, absorbing the blue part of the visible spectrum and allowing the yellow color to dominate. While many diamonds contain some nitrogen, it is the quantity and specific arrangement of these atoms that determine whether a diamond will exhibit a true yellow color or remain nearly colorless, with just a tinge of yellowish hue peeking through.

When nitrogen is present in significant amounts, a diamond transcends the typical color grading scale of D to Z and becomes classified as a fancy colored diamond. These fancy yellow diamonds are graded on a spectrum from Fancy Light to Fancy Vivid, with the intensity of the yellow color directly influencing their value. Despite their rarity, fancy yellow diamonds are more common than other fancy colored diamonds, offering a relatively affordable entry into the world of colored diamonds.

Blue diamonds derive their color from boron impurities in the crystalline structure. Boron absorbs yellow light and reflects blue, with varying concentrations creating different blue shades. Unlike most diamonds, which form closer to the Earth’s surface, blue diamonds originate from extreme depths – up to four times deeper. This deep formation process involves subduction, where the Earth’s tectonic plates move and bring blue diamonds closer to the surface over millions of years.

The famed Hope Diamond is a prime example of these extraordinary gems. Formed one hundred miles beneath the Earth’s surface, this 45.52 carat stone was carried upward by a volcanic eruption more than a billion years ago. It is a window to the past, brimming with rich history and fascinating provenance. Study of this particular blue diamond has revealed significant insights into the origin of blue diamonds, including how boron from ancient sea floors may have been transported to the surface.

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Pink and red diamonds stand apart from other colored diamonds. While most colored diamonds owe their hues to trace elements or impurities – such as nitrogen in yellow diamonds and boron in blue diamonds – pink diamonds gain their color from a phenomenon called plastic deformation. This process involves extreme pressure beyond what creates any other diamond, which distorts the diamond's crystal lattice and causes it to reflect red light. The more pronounced the deformation, the richer the pink hue. The strongest and deepest pink hues will appear red, and only 30 such natural red diamonds are known to exist in the world. Many pink or red diamonds do not survive this intense formation process and those that do are typically smaller in size. It is incredibly difficult and exceptionally rare to achieve high clarity and large carat sizes in these gems. The Williamson Pink Star, a cushion cut fancy vivid pink diamond weighing 11.15 carats, sold at a record-breaking US$57.7 million (HK$453.2 million at Sotheby’s in Hong Kong in 2022, setting an exceptional new world record price per carat for any diamond or gemstone and becoming the second most valuable jewel or gemstone ever sold at auction.

The majority of pink diamonds that exist today were sourced from the Argyle mine, located in northwestern Australia. Argyle pinks are particularly prized for their vibrant color saturation, attributed to densely-packed graining planes that emit a strong pink hue. In contrast, pink diamonds from other sources generally have lighter colors due to fewer and less distinct pink grainings. With the Argyle mine's closure in 2020, the rarity and desirability of these pink diamonds continue to rise, marking them as some of the most coveted gems in the world.

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