Last updated on December 2, 2021
While many of the basics of how to buy a diamond apply to all diamond types, they vary a bit among the different colours. Such is the case with natural blue diamonds, which are among the rarest and expensive in the family of fancy colour diamonds. Let’s take a look and find out which factors to consider to make a good investment.
What Are Blue Diamonds?
Natural blue diamonds are among the rarest of the fancy colour diamond family. They often owe their beautiful colour to the rare chemical element boron, which makes up only about 0.001% of the earth’s crust.
The natural blue colour developed when a small number of boron atoms penetrated nearby diamond crystals forming deep in the earth’s crust over millions of years and replaced carbon atoms in the diamond crystal lattice. It rarely happens because boron atoms are not usually present when natural diamonds form, and this is the reason blue diamonds are exceptionally rare.
Boron is one of the few elements that have atoms small enough to enter the diamond crystal lattice. However, the boron atom has one less available electron than carbon. The deficiency of electrons causes a defect in the diamond’s crystal structure and changes the way light travels through the stone. It causes the diamond to selectively absorb and transmit the light entering the stone, giving the diamond a blue colour.
It is worth mentioning that the presence of boron atoms in a diamond does not guarantee a blue colour as small numbers of nitrogen atoms in the diamond can produce defects and reduce the impact of boron. That is why rich blue colour diamonds contain very little nitrogen. The blue colour can also be caused by hydrogen-related defects and radiation exposure. Blue diamonds coloured by hydrogen defects are described as grey-blue to grey-violet, whereas those coloured by radiation exposure are usually described as green-blue.
Natural blue diamonds are found in only a few mines around the world. These sources include the Cullinan mine in South Africa, owned and operated by Petra Diamonds, and the Argyle mine (Rio Tinto) in Western Australia closed in 2020 because of the increasing operation cost and a stagnant diamond market. Once blue diamonds were mined in the Golconda mine in India.
Evaluating the Colour of Blue Diamonds
The colour evaluation of blue diamonds has three main components: hue, saturation and tone.
Hue is the visible colour of a diamond, and the primary hue of blue diamonds is blue. There can also be secondary hues that affect the value of stones. The most common secondary hues present in blue diamonds are grey and green.
Secondary hues that enhance the primary hue or do not detract from it add value as a rule, whereas secondary hues that detract from the primary one diminish the price. Natural pure blue diamonds with no secondary hues are the rarest and the most expensive as a result.
Saturation refers to the intensity of the colour. As a general rule, the more saturated the colour of a diamond, the more valuable it is. That is why diamonds with vivid blue colour are much more expensive than those with pale or faint colour.
Tone refers to how light or dark the colour is. The choice of the tone depends on your personal preference; however, the stones somewhere in the middle are the most sought-after.
A blue diamond’s colour grade is based on both the colour of the stone and its intensity level. According to the GIA, pink diamonds are classified using the following colour grades: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Vivid, Fancy Deep and Fancy Dark. The secondary colour is also included in the grade if present.
Evaluating the Clarity of Blue Diamonds
The clarity of blue diamonds is graded the same way as that of colourless stones. The fewer inclusions, the higher the clarity grade.
Of course, high clarity blue diamonds are more valuable, but this characteristic is not crucial for fancy colour stones. The blue colour tends to hide imperfections, so the appearance of blue diamonds is less affected by flaws compared to colourless diamonds.
When choosing the clarity of blue diamonds, look for a stone that is eye clean, meaning the diamond should not have inclusions visible to the naked eye. Blue diamonds in the SI1 – SI2 clarity range may look stunning and do not differ significantly from diamonds in VS or even the VVS range.
Evaluating the Cut of Blue Diamonds
The cut quality of blue diamonds, and all fancy colour diamonds in general, is not graded the same way as it is for colourless stones. Unlike colourless diamonds, fancy diamonds are not cut to maximize fire, brilliance and scintillation. These characteristics are considered to be secondary.
Blue diamonds are cut to maximize colour intensity, usually into fancy shapes. In other words, the proportions that are considered ideal for colourless diamonds will not always be the best to bring out the colour of blue diamonds.
Keep in mind that an excellent cut blue diamond costs a premium, so when choosing one, it is better to focus on the stone’s hue, saturation and tone and not judge the diamond using traditional cut grades.
Blue Diamond Rarity and Prices
Natural blue diamonds are one of the rarest colours in the fancy colour diamond family, and they are extremely expensive. Larger blue diamonds are even rarer and cost disproportionally more per carat.
The value of blue diamonds increases with colour intensity, as such stones are even rarer. For example, a 0.60-carat VS1 clarity fancy blue diamond can cost $126,000 and 0.50-carat VS1 clarity fancy intense blue diamond can cost $252,000. If you are looking for a relatively affordable option, you may want to consider a faint to light blue diamond or a blue diamond with grey and green secondary hues.
Due to the diminishing supply and increasing demand for blue diamonds, their price has been consistently rising between 12 and 17 per cent every year over the past decade, which is why fancy blue diamonds are considered a good investment and are highly sought after by collectors and connoisseurs.
Featured image: Igor Stratichuk, CC BY-SA 4.0, via Wikimedia Commons