De Beers Expert Shares Insights on Collecting Coloured Diamonds

It's expected that extraordinary diamonds would appear at Sotheby's auctions, but it’s a rare moment when collectors get the chance to acquire a unique gem like the De Beers Blue. The show-stopping 15.10 carat vivid-blue diamond, which is a major headliner at Sotheby’s upcoming auction in Hong Kong on 27 April, has created much buzz since the diamond was first discovered last year.

While white diamonds are widely viewed as the ultimate status symbol in popular culture, coloured diamonds appeal to a particular type of connoisseur. According to Sotheby’s, for every 10,000 gem-quality diamonds found, only one possesses colour. The odds are even lower for blue-hued diamonds, which are considered by experts as the most valuable among all fancy coloured diamonds. We sat down with Andrew Coxon, President of De Beers Institute of Diamonds, to find out more and to ask him to share his top tips for aspiring collectors.

Sotheby's: There have been many famous blue diamonds discovered over the years – what makes the De Beers Blue Diamond unique in comparison?

Andrew Coxon: Blue diamonds are Mother Nature’s works of art. The Cullinan mine is the finest source of blue diamonds in the world, but its diamonds are finite so it will not stay in production forever.

Newly discovered in April 2021, the De Beers Blue weighed an exceptional 39.34 carats as a beautiful vivid blue diamond in the rough. The value was beyond the means of most diamond manufacturers and the excitement so great that the owners of the mine decided to auction it to the highest bidder.

Great rarity will increase in value over time, like a rare painting. The sheer size, top quality and vivid colour of this diamond will excite many buyers, but what makes it more desirable for me, is its stunning beauty.

How are fancy coloured diamonds created?

The chemical compositions of blue, grey and yellow diamonds are different [to white diamonds] and occasionally quite unique. Molecules of boron create blue and grey colours, while nitrogen creates yellow diamonds. For brown, pink and red diamonds however, their hues are created by the distortion of the diamond’s atomic lattice during their 150-mile journey to the surface of the Earth. Ultra-high pressures and temperatures combine together to change the appearance. Green diamonds were exposed to ancient natural radiation whilst underground and that gives them their colour.

How do fancy colour diamonds compare with precious gemstones such as rubies and sapphires?

Diamonds are far rarer. There are many more sources of rubies and sapphires and their durability is much weaker than a natural diamond. For example, a diamond is four times harder than a ruby or sapphire and will stand the test of time much better. The youngest diamond is already 700 million years old and the oldest could date as far back as 3.5 billion years old.

Which fancy diamond colours are the most covetable?

It is a matter of personal taste but in terms of total value, blue diamonds are on top. In terms of price per carat, however, red diamonds, always smaller than five carats, are the highest, followed by green, pink then yellow.

How can potential investors determine the quality of a coloured diamond?

Think of the way you choose a painting, and you begin to understand the difference between choosing a fancy colour diamond. You need repetition, you need to see as many as you can, you cannot look at the paper and judge the real value. Like art, beauty in fancy coloured diamonds is in the eye of the beholder.

Do coloured diamonds have a grading system like their white counterparts?

There are 26 grades of cold to warm for white diamonds but only five hues for each fancy colour diamond. The colour is examined face up rather than face down which means that its colour can be concentrated by clever faceting.

The word “hue” is used to describe the fancy diamond’s dominant colour, rather than tint, tone or shade of colour. As Mother Nature is involved in its creation the result is a completely unique colour that the GIA has difficulty to describe.

This makes fancy coloured diamonds much harder to evaluate, especially as two fancy coloured diamonds with the same grading reports may have a difference in value of 50%. Like two paintings by a famous artist, both may carry the same signature, but one sells for double the price because it is more desirable.

Cut can affect the brilliance of a white diamond – does the same apply to coloured diamonds?

Because the GIA grade fancy colour diamonds from the face up, there are many ways of making the colour look better by intelligent faceting.

For example, a radiant cut can make a light-yellow look like a fancy yellow, face up. Extra facets around the culet will also concentrate the colour into the centre of the fancy coloured diamond in most shapes, except step cuts like emerald cuts. You cannot enhance the face up colour if you choose the emerald cut, so the original colour of the rough diamond has to be perfect before you decide to create a fancy colour emerald cut, like the De Beers Blue.

How important is size – is big necessarily better?

It is all about beauty, not size. However, if you do discover an exceptionally large and beautiful vivid colour diamond in internally flawless quality, buy it if you have the means, as you may never see it again in your lifetime!

What advice would you give new investors who are interested in coloured diamonds?

View as many fancy coloured diamonds as possible, and eventually your artistic eye will guide you. Look at what is available at auction or offered by brands – compare them, try them on, and have fun.

Beauty is remembered and enjoyed long after the price has been forgotten. In our business we learn the hard way. A cheap diamond is actually very expensive. If you buy it because it is cheap you will eventually discover why and then it’s too late. Buy what you fall in love with, and you will be happy ever after.