Learn: Buying Diamonds > Fancy Coloured Diamonds

What causes Colour in Diamonds?

Diamond is a very pure carbon that is crystalised under immense heat and pressure more than 100km beneath the earth’s surface. Sometimes other atoms are trapped in a diamond as it grows. Nitrogen is by far the most common; the tiniest amount can cause blue light to be absorbed giving the diamond a yellowish tint. They have been shot to the surface within hours by a volcano that picked the diamonds up along the way. They are ‘snap frozen’ – but if the journey takes too long, or is a stop-start affair, they can be dissolved or graphitized. Australia Argyle diamonds often show evidence of crystalline stress under magnification with polarized light and this is the likely cause of color as most are very pure carbon. The rare pink Argyle colour is thought to be caused by a tiny amount of hydrogen atoms caught up in deformities in the atomic structure.

Cutting Fancy Shaped Diamonds

The science of cutting FCD’s is very different from cutting colourless diamonds where fast changing contrast from dark zones to bright is what makes them sparkly and brilliant – the alternating bright dark bright flashes as you rock a white diamond. If a diamond has a dark zone in a photo then it probably will in real life too, and light leakage zones may not appear dark until the diamond is set.

Getting rid of dark zones also increases the depth of saturation of colours in a diamond. Apart from brown diamonds, almost all other colours are very pale and the more saturated and deeper tone the cutter can produce the more beautiful and more valuable the diamond will be. In the image, there is an example of the same carat weight and colour virtual diamonds showing how advanced cutting colour has become.

Fluorescence and Complimentary Colours

In simple terms, colours directly opposite each other on the colour wheel are said to be ‘complimentary colours’. When a diamond fluoresces with its complimentary colour it will appear less saturated when seen in daylight.
Blue and yellow are complimentary colours; red and cyan are complementary; and so are green and magenta.

Mixing two complimentary colours of light together gives you white or grey. Blue fluorescence can make a yellow diamond paler or less saturated and reduce its value. Yellow diamonds that fluoresce yellow will be a stronger yellow in daylight which has more UV light. Green diamonds that fluoresce yellow are highly sought after, they seem to have a radioactive glow. Unfortunately, yellow diamonds more commonly fluoresce blue and are sold at a lower price.

All or almost all pink, champagne and colourless Argyle diamonds, are strongly blue fluorescent. This is an advantage in the case of pink diamonds because purplish pink diamonds are more valuable than straight pink. Fluorescent brown or champagne diamonds become a shade lighter in daylight.

FCRF Fancy Color Diamond Index.
Image Source: Fancy Color Research Foundation – FCRF, www.fcresearh.org

Carat weight has a similar impact on pricing the same as colourless diamonds. Arguably, snob carat weights, like 1ct, 5ct, have more impact on collectible diamonds as buyers are often focused on the potential resale value. Fancy yellow diamonds are found with similar size distributions to colourless diamonds, but natural blue diamonds are very pure type II with a minuscule amount of boron that causes the color. Type II diamonds are often found in very large sizes and so there are quite a few very large blue rough diamonds found each year. (Argyle grey-blue diamonds are an exception and are mostly very small.)

Clarity, as mentioned elsewhere has less impact on pricing than colourless diamonds.

The owner who submits a FCD to GIA can request a ‘partial cert’, which does not mention the clarity grade (and some other factors). Buyers usually take this to mean the stone has a clarity of I1 or lower. In some cases, the vendor may communicate the diamond has an I1 grade while buyers might argue the diamond is an I2. There are many million-dollar FCD’s with grades as low as I2, but very few GIA full cert graded I2 or I3 diamonds!

A ‘half cert’ is proof that GIA considers the diamond to be natural and the colour is untreated. A lot of other very important information is also missing, and this allows diamond cutters to get away with blue murder. It makes sense that a seller would not want to declare that a diamond has an imperfect grade, given that many low clarity rare coloured diamonds fetch 7 figures. Buyers should beware that a half cert does not include polish and symmetry grades which are often very poor. There are no cut quality grades for even round diamonds and across the board cut quality is notoriously bad. Fluorescence is not mentioned and can cause a marked reduction in apparent colour.

The ‘double certed’ diamond in the table is the very first larger than one carat vivid pink diamond ever mined at Argyle. The diamond is from samples at Smoke Creek taken to prove the economic viability before Argyle was even named (after nearby Lake Argyle). I purchased it from Bill Leslie, who at the time was a company lawyer and a director of Ashton Mining who discovered the mine.

Colour unsurprisingly is the all important value factor. Consider that there are 17 grades for D-Z colourless diamonds where as for yellow diamonds there are only six and pink, blue, orange and green there are nine. This means the price jumps at grade boundaries can be very large, more than double in extreme cases.

Colour Science

Colour can best be described as three-dimensional, it is very complex. Most people try to describe colour by the hue and the light or darkness, however, you must also describe the saturation or bright to dullness.

The Munsell colour wheel shows how Hue, Tone, and Saturation work together.

A good analogy for understanding colour is to consider an imaginary concept of traveling through the centre of the earth in an elevator with windows all around. In the center of the earth, we look out and see all the Hues around the ‘equator’ – all the colours of the rainbow with violet joining up nicely with the plum colour. As we go up things get lighter, and if the elevator descends all the way to the south pole all we see is blackness. That is tone; lightness to darkness. If we go back to the center of the earth and step out onto that floor, walk out towards the red direction, the saturation of the red gets more intense. If we look up to the floors above we see pink, and down we see burgundy.  When we arrive at the equator, we see vivid red. Looking to our right, we see really bright orangish red and to our left things turn plum coloured.

To make things a little more complex, the equator is not a circle. For example, red and green colours can be more saturated than blue and yellow. Then there are secondary colours or hues that impact attractiveness. Warmer colours on the red to the green side of the ‘colour world’ can have a brownish duller undertone and the blue cooler side can be greyish. Sadly, blue diamonds all suffer from a bit of greyness and are never quite as richly saturated as the finest sapphires.

A yellow diamond with a green secondary hue is graded as “Fancy Greenish Yellow.” A yellow diamond with a darkish tone might be called “Fancy Brownish Yellow” or if it is duller still, it may be graded as “Fancy Yellowish Brown” and suffer an even bigger price drop. Secondary hues in yellow diamonds include orangish greenish yellow (often slightly cheaper) and orangish yellow (can be more expensive – pure orange is exceptionally rare and very costly).