How Do Diamonds Get Their Fancy Colors?

From brilliant blues to fiery reds, discover how nature crafts diamonds in every color, and why some shades are rarer than the rest

Imagine a diamond glowing like molten gold, blushing in rose petal pink or shimmering with a deep, oceanic blue.  While we often picture diamonds as flawless, clear gems set in engagement rings, colorful diamonds — one of nature’s rarest and most captivating phenomena — dazzle with hues that rival the rainbow. 

Starting today, visitors at the National Museum of Natural History will have the opportunity to view one of the finest collections of diamonds ever amassed, each bestowed with a coveted “Fancy color” grading by the Gemological Institute of America. The Winston Red Diamond and Winston Fancy Color Diamond Collection were gifted to the museum by Ronald Winston, the son of distinguished jeweler and gem collector Harry Winston. In 1958, Harry Winston donated the iconic Hope Diamond to the Smithsonian, laying the foundation for the National Gem Collection.

National Treasure: Revealing the Stunning 2.33-Carat Winston Red Diamond

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“Only 1 in 10,000 diamonds is a fancy color diamond,” said mineralogist Gabriela Farfan, the museum’s Coralyn W. Whitney Curator of Gems and Minerals. “In this collection, we have diamonds in colors I could never have dreamed of, including elusive reds, violets, oranges and greens.”

What geological processes cause diamonds to appear in such a diverse range of colors? The answer lies miles beneath the Earth's surface, where diamonds are formed when intense heat and pressure force carbon atoms into rigid crystal lattice structures. However, this journey isn’t always flawless. Trapped elements and shifts in pressure can introduce unique characteristics to the gems, including a brilliant array of hues that span nature’s color palette.

Yellow Diamonds: Common but Captivating

While diamonds are made almost entirely of carbon, nature often adds a twist — nitrogen. This impurity subtly tints many diamonds, introducing soft complexions of yellow to otherwise colorless gems.  While yellow is the most common hue among colorful diamonds, very few have a bright enough shade to catch the eye of mineralogists and gem collectors.

However, when nitrogen atoms are arranged just right within a diamond’s crystal structure, something extraordinary happens. The yellow becomes vibrant enough to earn the coveted “fancy color” designation.  These diamonds, glowing in rich shades from buttery gold to warm amber, stand out from their paler counterparts.

Blue Diamonds: The Hue of the Hope

The iconic Hope Diamond is the centerpiece of NMNH’s gem collection, and the bright blue stone has mesmerized over 100 million visitors with its beauty. Among the rarest and most fascinating gems on Earth, blue diamonds owe their vibrant hue to an unexpected element — boron. Even the tiniest amount of boron can change the color of an entire diamond.

“The Hope Diamond has only trace impurities of boron, which have turned the diamond a stunning shade of blue,” said Farfan. “Among the millions of atoms in a diamond, only one needs to be a boron atom to color the entire gem.”

When boron atoms integrate into a diamond’s crystal structure, they absorb yellow light, allowing only blue to shine through. Subtle variations in boron concentration can create countless different shades, from icy teals to deep oceanic tones.

Red and Pink Diamonds: The Rarest of Them All

Among the world’s most coveted gems, red and pink diamonds are truly a sight to behold, with delicate hues ranging from light blush to deep crimson. But their beauty is matched only by their rarity, as these natural wonders are the scarcest diamonds on Earth.

While most colorful diamonds get their pigmented appearance from atomic impurities, red and pink diamonds are the product of extremely high pressure and temperature conditions deep within the Earth.  These geologic processes cause a phenomenon called plastic deformation, where the entire crystalline structure of a gem is strained and altered, allowing it to reflect red light. The more intense the pressure, the richer the shade. But this comes at a cost. The force often compromises clarity and carat weight, making high-quality red and pink diamonds exceptionally rare.

Taking center stage in the museum's new diamond collection is the dazzling Winston Red Diamond. Researchers estimate that less than one in 25 million diamonds is a Fancy red, and the Winston Red Diamond is one of the most exquisite in existence.

“At 2.33 carats, the Winston Red Diamond is one of the largest red diamonds in the world,” said Farfan. “This is a brilliant gem and an extremely significant donation to the museum’s National Gem Collection.”

Green Diamonds: Radiation Pigmentation

Casting an otherworldly glow, green diamonds are distinguished by their vivid coloration and the extraordinary conditions that create them.  Unlike other colorful diamonds, their vibrant tones come from exposure to natural radiation.

Over millions of years, decaying radioactive elements emit energy that disrupts the diamond’s crystal structure, causing vacancies, or holes, to form. This microscopic transformation allows the gems to absorb red and yellow light and reflect green. Diamonds can also be artificially treated with radiation to achieve these envious shades of green.

Every Color of the Rainbow

Fancy color diamonds come in an astonishing array of shades, with natural forces combining in unique ways to produce nearly every hue imaginable. Just like mixing red and blue paint creates purple, various geological processes can work independently or blend together, resulting in a spectrum of colors.

The Winston Red Diamond will be displayed alongside 40 other gems from the Winston Fancy Color Diamond Collection. The diamonds will be arranged in a radiant rainbow of color, featuring unique shades from deep teal to soft peach.

“These gems will give us the opportunity to share with our visitors the full range of colors in which diamonds occur,” Farfan said. The Winston Red Diamond and Fancy Color Diamond Collection are the result of 60 years of dedicated acquisitions by Ronald Winston and are now on display in the museum’s Harry Winston Gallery. Alongside the Hope Diamond, the new display will showcase the brilliance and rarity of these extraordinary gems, offering a dazzling window into the mysterious geologic forces that shape the Earth.

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Emma Saaty | Read More

Emma Saaty is a Science Communications Specialist at the Smithsonian National Museum of Natural History.  She brings science to the public by covering natural history research for Smithsonian Magazine's, Smithsonian Voices.  Additionally, she tracks media coverage and coordinates filming activities for the museum’s Office of Communications and Public Affairs.  Emma recently completed her Bachelor of Science in Biological Anthropology with a minor in Journalism at George Washington University where she conducted research on Virunga mountain gorillas with GW’s Life History and Skeletal Biology laboratory.  You can find her here.