How do colored diamonds come about? They lose color after being polished!

Diamonds are rare and precious, and are even equated with loyal love. Indeed, when blingbling diamonds appear before our eyes, few people remain unmoved, unless they own more beautiful colored diamonds!

Colored diamonds, rare and expensive

Colored diamonds are diamonds with a noticeable color. For yellow or brown diamonds, the color must be a certain concentration, bright enough to be called a colored diamond. For other colored diamonds, a lighter color can also be called a colored diamond. Generally speaking, the more intense the color of a colored diamond, the higher its value.

Among the many colored diamonds, red and green diamonds are very rare, and most colored diamonds are yellow and brown diamonds.

The geological conditions for the formation of colored diamonds are very special. For example, the only stable source of pink diamonds in the world is Australia. In Australia's Argyle Mine, only one colored diamond can be obtained for every 100,000 rare white diamonds produced. Compared with the rarity of colored diamonds, the mining of colorless diamonds has long been globalized. It is precisely because of their rarity and beauty that the value of colored diamonds has skyrocketed. The record high selling prices repeatedly set in the auction market cannot stop the crazy pace of collectors.

How valuable are colored diamonds? At a 2018 auction, Sotheby's sold a 5-carat Fancy Intense blue diamond, and the buyer paid HK$108.48 million for the beautiful stone; and last November, Christie's auctioned an 18.96-carat Fancy Vivid pink diamond for more than 50.37 million Swiss francs, or more than RMB 300 million.

Sotheby’s “Love” Fancy Vivid Blue Diamond (left) and Christie’s “THE PINK LEGACY” Fancy Vivid Pink Diamond (right) | @Sotheby’s Auction House (left), @Christie’s International (right)

The source of diamond color

The essence of diamond is the element C (carbon). In a pure carbon diamond crystal without any impurities, each C atom is connected to another 4 C atoms by covalent bonds. This structure makes diamond have very stable chemical properties.

This inflatable tent can be set up in one minute. Its design is inspired by the molecular structure of diamonds. Doesn’t it have both beauty and stability?

In the long geological process, only a few diamonds contain only C elements, and most diamonds contain a certain amount of N (nitrogen). N elements can cause diamonds to turn yellow, but if the yellow is not bright enough, the diamond will not reach the level of colored diamonds, which will reduce the value of the diamond. Therefore, gemologists classify diamonds into different grades according to the degree of yellowing. To a certain extent, the whiter the diamond, the more valuable it is.

To understand how the N element makes diamonds yellow, we must first understand the existence form of N atoms inside diamonds.

N atoms have different states in diamonds. N atoms in natural diamonds tend to live in groups. When two N atoms form a pair, they will cause the crystal structure inside the diamond to distort, resulting in structural defects. This defect can absorb light of different colors and is called a "color center."

In addition to N atom pairs, when three N atoms are aggregated together, a vacant position without an atom in the middle will also form a color center. Both color centers can absorb blue and purple light in visible light, making diamonds appear yellow. When 4-9 nitrogen atoms in diamonds are together, they can even aggregate into thin sheets. In short, N atoms in different aggregated states can form different color centers, resulting in different absorption of visible light. The different shades of yellow are the masterpiece of the N element.

The 128.54-carat Tiffany yellow diamond was once set in a ribbon necklace worn by Audrey Hepburn. The necklace was designed by the famous designer Jean Schlumberger.

The attractive blue color of blue diamonds is mainly due to the presence of B (boron). When a B atom replaces a C atom in the diamond lattice in an isolated state, a color center is formed, which absorbs red, yellow and green light in the visible light, while blue and violet light are not absorbed, so the diamond shows a beautiful blue color. In addition to producing beautiful colors, B can also cause wonderful changes in the properties of diamonds. Natural diamonds are not conductive, but when B atoms replace C atoms, electrons that can move freely are generated in the diamond, making it weakly conductive. This is also one of the bases for identifying whether a blue diamond is natural or not.

The world's largest deep blue diamond "Hope" is said to be an ominous diamond that will bring bad luck to its owner.

The pink color of pink diamonds, which are loved by people, is related to the changes in the internal crystal structure. During the formation and migration of diamonds, the internal structure of the crystal may be dislocated, resulting in structural deformation. This change, known as "plastic deformation", not only causes crystal structural defects, but also changes the aggregation rate and form of the N element in the diamond, causing the diamond to form different colors. The colors of natural brown, pink and purple diamonds are all related to the plastic deformation of diamonds.

At Sotheby's, the 24.78-carat pink diamond seemed to overwhelm even the models.

Green and blue-green diamonds are usually formed due to long-term radiation. When the energy of the radiation is high enough, the diamond crystal structure is damaged and defects are generated, which causes a series of new light absorption, causing the diamond to appear green. If the irradiation time is long enough or the radiation dose is too high, the diamond will turn dark green or even black. Lattice damage caused by radiation may also form blue or yellow-brown diamonds. The thickness of the color of natural green diamonds is only about 20 microns, and they often have no color after cutting and polishing. They are "unbearable" gems.

The world's largest green diamond, the Dresden Green Diamond weighing 40.70 carats, is particularly rare because it still shows a bright green color after polishing.

However, natural beautiful colored diamonds are often difficult to obtain, unless you are a big collector active in major auctions. If you want to buy natural colored diamonds, save money first!

Author: Nine Knights

An AI

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