Out of every known place where diamonds are found—in the past and the present—India, Indonesia, Brazil, South Africa and Australia produce the most significant quantities of coloured diamonds.
One of the first coloured diamonds to be introduced to the world is the famous French Blue, which was bought by Jean-Baptiste Tavernier (1605-1689) in Mogul India. It later became known as the Hope Diamond. India has produced probably more blue and light pink diamonds than any other known place on earth. Brazil and other diamond producing mines in Africa came along later as alternative sources of coloured diamonds.
Australia is now a big player in coloured diamonds. Australian production is made up of the cape and brown series (colourless to tinted diamonds). Beauty characterises their uniqueness. Today there is a greater range of colours than ever—aqua-blues, intense yellows, sweet pinks, pink browns, browns, greens, red and purple (the last being extremely rare), all of which represent nature’s patient work over millions of years.
It was in 1984 that the first pink diamonds from Australia’s Argyle mine began to show up in the new market for coloured diamonds. Pink diamonds are rare, costly and very desirable. The rich pinks to purple pinks are signature colours of the Argyle mine.
When viewed in a face-up position, Argyle’s pink diamonds tend to have numerous minute pink grain lines embedded closely together in the crystal. This is the reason for the stones’ pleasing and concentrated pinkness. Experts believe that these may be a result of the diamond crystals undergoing ‘plastic deformation’ by geological pressures exerted on them in the earth or during their rise to the earth’s surface create.
The more exceptional pink to red diamonds are sold individually by invitation-only special auctions known as ‘tenders’ in New York, Sydney, Tokyo, Hong Kong, London and Geneva. About 40 to 50 carats of diamonds weighing less than 3 carats each are sold at these auctions annually. Bids can hit prices in excess of US$100,000 per carat. Of every million carats of rough diamonds produced by a mine, roughly only 1 carat is suitable for these auctions.
The majority of diamonds produced at Argyle are brown diamonds, with the remaining being yellow to near colourless and colourless. The very rare pink, grayish blue, and green diamonds make up less than 1 per cent.
As a result of the large number of brown diamonds Argyle produces, a marketing campaign for ‘champagne’ and ‘cognac’ diamonds was introduced, and proved quite successful. A C1 to C7 scale is used to rate increasing intensities of brown.
With pink diamonds, Argyle uses four categories of colour: pink, purplish pink, brownish pink, and pink champagne. The stones are graded according to their colour intensity, from very faint to very intense.
In order to build product demand, the Indo-Argyle Diamond Council was launched. This partnership with a number of Indian jewellery manufacturers has helped to promote coloured diamonds around the world. Coloured diamonds are now widely recognized internationally.
For clear and easy communication, experts in diamond research have categorized diamonds into different types ranging from Type Ia (the most common) to IIb (the most rare).
DIAMOND TYPES
Type Ia: Approximately 98 per cent of all natural diamonds are of this type. These contain relatively large amounts of nitrogen distributed in aggregates of small groups of nitrogen atoms. These diamonds range in colour from colourless to pale yellow. They are also called ‘cape diamonds’ as they show the distinctive cape spectrum when analysed by a spectroscope.
Type Ib: These account for less than 1 per cent of diamonds in nature. They contain smaller amounts of nitrogen, but this is evenly dispersed throughout the stone as single atoms. Such diamonds have a deep yellow colour and are often called ‘canaries’ because of it. They do not show the cape spectrum.
Type IIa: Diamonds of this type are extremely rare. They do not contain enough nitrogen to be detected with standard gemological methods. They are usually near colourless.
Type IIb: These are the most rare of diamonds. They are thought to contain more boron than nitrogen and are electrically conductive. A conduction test is diagnostic for type IIb diamonds. Their colour is usually blue to gray or more rarely, near colourless.
Today, diamonds are routinely irradiated on a commercial basis to produce green and blue colours. With proper heat treatment, a range of colours such as yellow, pink and brown can be produced to meet industry demand. Recently, the fashion trend in black and white diamond jewellery has led to an increase in very dark green or black irradiated diamonds.
There are two main methods of irradiating diamonds:
1. Electron irradiation: this uses high-energy electrons from an electron accelerator to produce a greenish-blue stone. The process rarely carries any risk of radioactivity,
2. Neutron irradiation: fast neutrons from a nuclear reactor are used to enhance stones from dark green to black. While they do carry the potential for radioactivity, this is extremely rare. Many treated black diamonds sold today are neutron irradiated.
Developments In Treatment Technology
Nova Diamond markets their HPHT (High Pressure High Temperature) treated yellow green diamonds by certifying and laser inscribing them with a Nova Diamond™ logo and a unique serial number.
A US company, InColor Enhanced Diamonds, has developed a new colour treatment that can change low quality, colourless, yellow or brown diamonds to ‘Jet Black’ or ‘Dresden Green’. These stones owe their colour to an ion implantation that changes the surface to green or black, depending on the treatment.
An Israeli company, First Diamond Group, has developed a colour treatment that imitates the ‘chameleon diamond effect’. This treatment gives cape colour diamonds an intense fancy yellow that shifts to fancy greenish yellow or green under different lighting conditions. No residual radioactivity has been reported.
The General Electric/Lazare Kaplan International (GE/LKI) partnership has also been marketing HPHT treated diamonds using the GE brand name ‘Bellataire’™. These near colourless HPHT treated diamonds come with certification and the inscription ‘GE POL’.
There are other suppliers known to be producing HPHT treated yellow green diamonds, but not all their diamonds are certified or inscribed.
Synthetic Coloured Diamonds
Gemesis Corporation, a Florida-based company, has succeeded in producing coloured and near coloured synthetic diamonds. Other suppliers include Morion Company and Lucent Diamonds. Since 1990, Russia, with its technical knowledge and low labour costs, has also become a producer of synthetic diamonds for jewellery.
Fancy coloured synthetic diamonds are sold below the price of similar quality coloured natural diamonds. Most synthetic diamonds are small and coloured.
The majority of colour enhanced diamonds are treated in laboratories of international standards in North America. In the US, most colour treatment facilities follow NRC (Nuclear Regulatory Control) procedures with awareness of the consequences if treatments are not conducted safely. That’s why disclosure is requirement for all coloured diamonds, treated and untreated. In reality, this is not always the case. Good consumer protection laws exist n the US and Europe. Guidelines exist in Asia, Africa and South America but are not always effective.
Gemological characteristics
Electron irradiated diamonds: These appear bluish green to greenish blue. They are easily distinguished from natural blue diamonds because they are electrically conductive. Faceted diamonds may show ‘umbrella’ colour zoning around the culet (the point at the bottom of a diamond) if irradiated from the pavilion, or more intense colour near the crown if irradiated through the face of the stone. A properly equipped gemological laboratory can identify the origin of colour of a diamond.
Neutron irradiated diamonds: A strong fiber optic light source should reveal the dark green colour of diamonds treated by neutron irradiation to make them look dark green to black. A properly equipped gemological laboratory can detect the radioactivity.
Ion implantation: The colour treatment is done on the surface of a diamond. Colour is unevenly distributed with unnatural surface iridescence.
Judging quality
Colour: This is the key factor with all fancy coloured diamonds. However the grading process is very subjective. Objective colour grading requires a mechanism for consistent observation and established colour references with suitable master stones. Generally, clarity and cut have less impact on value.
The origin of colour has a strong impact on price. Today, identifying the natural colours of fancy coloured diamonds are a challenge. Only a fully equipped gemological laboratory with expertise in natural coloured diamond analysis can identify them.
The colour of a stone is graded on a face-up position. Quality grading depends on hue, intensity of colour with pleasing tone and an even colour distribution.
How hue is described can make a lot of difference in price. It is also important to know the terminology for describing the colour variances that interest you, the available colour shades and its rarity and value. For instance, the colour of a fancy yellow diamond might be described as yellow, orangish yellow or brownish yellow like in yellow sapphires.
Primary and secondary hues affect colour gradation. Some colour combinations are rare and more expensive than others. The popular pink and yellow diamonds are generally less intense in colour while a brown, which is a highly saturated orange, has a strong body colour due to its high tone.
Tone, described as relative lightness or darkness, also influences overall colour. What makes a coloured diamond desirable is its brilliant flashes among less bright flashes. Yellow and pink diamonds should display more yellow and pink brilliance flashes respectively. Diamonds of intense colour, such as the ruby red, sapphire blues and emerald greens, are extremely rare. They are the most expensive of all gemstones. Fancy black diamonds, typically opaque, are less expensive than other fancy colours. Fancy white diamonds, usually milky or cloudy in appearance, are less desirable and therefore less expensive.
It is also important to know how diamond reports classify the intensity of colour. This can be faint, very light, light, fancy light, fancy, fancy dark, fancy deep, fancy intense and fancy vivid. The tonal differences affect the value of a diamond.
Lately, HPHT (High Pressure High Temperature) techniques can be used to produce off-white and brownish diamonds into a variety of fancy colours from yellowish green and greenish yellow to shades of pink and blue. Some of these colours are difficult to distinguish from the natural. It is highly recommended to obtain a laboratory report for any fancy coloured diamond.
Clarity: Clarity is graded on the same criteria used for colourless diamonds. Generally, flawless (10x magnification) natural coloured diamonds are rare. The clarity is graded slightly imperfect/included and imperfect/included.
Clarity enhancements such as fracture filling and lasering of black inclusions (bleaching of dark included crystals in order to make them less visible) are also common.
Cut: Some shapes that are common among coloured diamonds can influence overall brilliance and intensity of colour. Since size and shape of the rough determines the final cut, the password is flexibility. Some shapes are rare and difficult to fashion, while other shapes are easy in any colour. Emerald cut is difficult to find, and sometimes even round brilliant cut in a particular colour is even more difficult. Lately, radiant and princess cuts have become popular because cutters have found a way to maximize the brilliance of flashes through a combination of shape, proportions and facet alignments—elements that give a diamond its life.
Telling The Difference
It can be both easy and difficult to tell a colour treated diamond from a natural one. It is easier to see the difference between the greens, pinks, reds and blues. It gets more difficult to tell the natural apart from the treated when the diamonds are small. Usually the low price and their easy availability are an indication. Large stones should come with a lab report on origin of colour.
Colour treated diamonds are relatively cheaper than their natural counterparts but prices depend on the suppliers’ cost, brand, marketing, mark-ups and location to mention a few variables. There are no published price lists like the Rapapport Diamond Report or The Guide (both US publications) for coloured and treated diamonds.
Dealers who work directly with manufacturers know the mark-ups. Buyers may not know the true identity of the stones they buy and that’s why branding has become a marketing tool to educate consumers. Disclosure is the password for consumer confidence.
Disclosure
The US Federal Trade Commission (FTC), Jewelers Vigilance Committee (JVC), CIBJO and other trade organizations believe that the failure to disclose treatment information is deceptive, and that all treated stones sold must be disclosed without fail.
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