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Fancy Coloured Diamonds
While the most common diamonds are colourless, diamonds also come in a range of colours due to trace elements impurities like nitrogen, boron, and structural irregularities which produces fancy colours like yellow, brown, pink, blue, green, red to name a few. Fancy coloured diamonds are graded considering three factors: the diamond's basic body colour, its intensity, and evenness of colour.
A more intense diamond is usually rarer and therefore more valuable than a less intense diamond of the same colour, all other parameters being equal.
The GIA recognises grades the intensity of fancy coloured diamonds from 'Faint' to 'Fancy Vivid', using the following scale: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Dark, Fancy Deep and Fancy Vivid.
Yellow: When a diamond's body colour is more intense than the Z colour grading on the normal colour range, it is graded to what is known as a fancy yellow diamond. Fancy yellow diamonds are so coloured due to the presence of nitrogen in the stone. Yellow and brown diamonds are most commonly available diamonds.
Pink: Pink diamonds are rarer than yellow or brown ones, with the Australian Argyle Mine being one of the few major mines where they are found. Their colour is caused by irregular crystal growth patterns that cause microscopic imperfections within the lattice structure.
Red: Red diamonds are among the rarest coloured diamonds to be found, most commonly found in famous Argyle mines in Australia. For a natural red diamond, the price can be as high as one million dollars per carat.
Although inclusions in colourless stones reduce the stone's value, they rarely have an impact on the value of a fancy coloured diamond. Colour and intensity being the most important value factors for a fancy coloured diamond.
Diamonds may be treated to enhance their colour, to improve their clarity, or both. These diamonds are typically low in quality and are treated to make them more attractive or desirable. Few of colour treatments are as below:
Irradiation: Irradiation is a process in which a diamond is treated with subatomic particles with a cyclotron, which was introduced in the mid-1900s. It produces shades of green, blue-green, or blue coloured to diamonds. However, diamonds irradiated with a cyclotron can show colour zoning, or uneven distribution of colour. Irradiation with a linear accelerator produces a uniform colour, without light or dark patches or spots, throughout the diamond.
Annealing is another colour enhancement process that often accompanies irradiation. In annealing, the diamond is heated and then cooled in a controlled process to further modify the colour of the already irradiated diamond. Irradiation followed by annealing can create brown, orange, or yellow diamonds. The colour of an irradiated diamond can be changed by heat, therefore extra care must be taken during repair, re-cutting or re-polishing.
Coating: Coating refers to the process whereby the surface of the diamond is coated to hide its undesirable colour. Coating is generally done by ultra thin layer of chemicals or plastics.
HPHT: stands for High-pressure High-Temperature treatment. It can change the unattractive body colour of a diamond into one that is more desirable such as pink, blue, yellow, or green. This treatment is so complex that it is virtually impossible to detect this outside a well-equipped laboratory.
The most common types of treatment to improve the clarity of a diamond are laser drilling and fracture filling. Both of these treatments became popular during 1970’s when advancements in diamond cutting were developed
Laser drilling: Laser is commonly used to create a tiny passage in the diamond to reach the inclusion. Once the inclusion has been made accessible, it can be vaporised, or bleached to remove or lighten it. The laser drill-hole cannot be seen with the naked eye, but is usually visible under 10 x magnifications.
Fracture Filling: This is the most common type of clarity treatment today. In fracture filling, molten glass is used to fill the diamond's surface reaching fractures and improves its apparent clarity. The type of filling substance used ensures that the fracture cannot be seen to an untrained eye. However, fracture filling can be detected if it causes trapped gas bubbles, if the filling substance has crackled texture, or by evidence of a flash of colour under certain lighting conditions and magnification. This is treatment is not permanent and can be easily damaged if not handled properly.
A diamond simulant is a material which looks like a diamond having different chemical, optical and physical properties from a diamond. There are several diamond simulants that are available in the market for prices far below that of a natural diamond. While a natural diamond is made of carbon in nature, simulants are mostly made in a laboratory. Some simulants can be natural material.
An expert gemologist can differentiate between a natural and a simulant after examining the stone. While purchasing a diamond, ensure that it is certified by a reputable grading laboratory as being a natural diamond.
Cubic zirconia: One of the most common and popular diamond simulants is the cubic zirconia. Created in a laboratory, cubic zirconia is a cubic form of zirconium oxide. It tends to chip or turn yellow over time.
Moissanite: In 1995, a US company developed synthetic moissanite from silicon carbide crystals, as the mineral is extremely rarely found naturally and was originally discovered in meteorite fragments. Moissanite costs one-tenth that of a diamond.
Colourless Sapphire: Pure corundum is colourless and is known as colourless sapphire. Corundum is second to diamond in hardness, making the colourless sapphire a popular choice as a diamond substitute since the stone is extremely durable. Colourless sapphires are becoming exceedingly rare in the market as companies that colour treat pure corundum are purchasing the majority of the stone. Synthetic colourless sapphires are more easily available.
YAG: Yttrium aluminium garnet is a man-made material often used as a diamond simulant. Its physical properties are similar to that of a natural garnet. Along with Gallium-Gadolinium Garnet, YAG was often previously used as a diamond simulant but has largely been rendered obsolete by cubic zirconia.
Rhinestones: It’s a common misconception that rhinestone is a stone is a crystal. It is an artificial stone of high lustre made of glass, paste and is foilbacked. They can be coloured or colourless, and the clear rhinestones are often used as diamond simulants.