What are Treated Diamonds?
Natural diamonds are those that are formed deep under the earth’s crust over millions of years, completely by nature without any human intervention.
In contrast, synthetic diamonds are man-made diamonds, created in a laboratory in just a few hours or days. Both natural diamonds and synthetic diamonds can also undergo a variety of “treatments,” which are artificial processes that diamonds may undergo to enhance certain quality characteristics, more specifically their colour or clarity.
Diamonds are treated in order to make flaws appear more attractive and marketable. These treatments alter a diamond from its natural state, and therefore must be fully disclosed as diamond treatments significantly affect the value of a diamond.
Most diamond treatments are unstable – in other words, they are not permanent, but reversible. For this reason, all internationally accepted rules for diamond grading forbid the certification of treated diamonds (with the exception of one treatment for enhancing clarity called ‘laser drilling’, described in the following discussion on the various methods of treating diamonds).
DCLA and other reputable diamond grading laboratories do not issue diamond grading reports on treated diamonds. A letter identifying the treated diamond may be issued, but it will not include quality characteristics.
Diamond Clarity Treatments
Diamonds often have dark inclusions present, usually consisting of graphite or sulphide, or other iron-containing minerals. These dark inclusions become present in the diamond during its natural growth formation. For obvious aesthetic reasons, diamonds with visible dark inclusions are less desirable than those with light or transparent inclusions.
Diamonds with surface-reaching black inclusions are often deep boiled under pressure in strong acids, as the mineral inclusions described are all dissolved by these acids without affecting the diamond material itself. Deep boiling forces the acid deeper into surface-reaching cracks of the diamond, allowing more of the black material to be reached. But what happens when a dark inclusion is completely sealed inside the diamond? There are currently two known methods for reaching such inclusions, traditional laser drilling and
1 . Traditional Laser Drilling
Laser drilling is the process of drilling a hole with a hot, high-power laser beam from a point on the surface of a diamond to a dark inclusion trapped within the diamond. The pulsed, focused beam vaporises a tiny channel, or ‘drill hole’, to the dark inclusion; this provides a conduit to the inclusion from the surface, and deep boiling in acid or bleach will remove the dark and cause the inclusion to be less visible. The drill holes themselves appear as fine, straight tunnels from the surface of the diamond to an inclusion.
According to internationally accepted rules for diamond certification, laser drilled diamonds are allowed to be certified because the treatment is permanent – it will not change or revert back to its original state. However, the treatment must be clearly stated on the certificate; laser drilling may improve the appearance of a diamond, but it also reduces its value.
2 . Internal Laser Drilling (Km treatment)
KM stands for the Hebrew phrase ‘kiduah meyuhad’, meaning ‘special drill’. Rather than burning a hole to a dark inclusion from the surface like with traditional laser drilling, a very hot laser is focused on the internal inclusion itself. The heat causes the inclusion to expand, and creates small channels from the inclusion to the surface. As with traditional laser drilling, once a channel to inclusion is created, the dark inclusion can be bleached out with a strong acid.
KM internal laser drill holes can vary in appearance. Some look slightly irregular worm holes, or step-like channels. Others appear with disc-like features, with irregular boundaries. In any case, careful gemological examination will conclusively identify the treatment.
As with traditional laser drilling, the treatment of diamonds with KM internal laser drilling is permanent. Thus, KM drilled diamonds are also allowed to be certified, according to internationally recognised standards for diamond certification, but the treatment must also be clearly stated on the certificate as the treatment reduces a diamond’s value.
Fracture filling is a clarity treatment whereby a glass-like resin is injected into white, often bright feathers or fractures that reach the surface of the diamond. The fractures do not disappear, but the film creates an optical illusion that makes them less visible to the naked eye.
How does it work? Feathers are visible when light reflects off of them; by filling them with a resin, light is able to travel through the feather, making it less visible. Some diamonds may first be laser drilled to reach a feather that does not reach the surface; the filling is then injected through the created channel and sealed.
Fracture filled diamonds can be identified by a trained gemologist under magnification. The most prominent feature of fracture filled diamonds is the presence of a ‘flash effect’, or bright vivid streaks of colour from the filled fracture. These colour flashes are the result of differences in dispersion between the diamond and the filling material. Other identifying characteristics in the filling are gas bubbles, flow structures, and a ‘crackly’ type of texture in the filling material.
Fracture filling is not a stable diamond treatment; the process is reversible and easily altered by heat. Jewellery repairs, diamond resetting, diamond cleaning, and even sunlight can erode the filler or darken its colour. For this reason, DCLA does not issue diamond grading certificates for fracture filled diamonds.
Diamond Colour Treatments
Surface coating is the process of adding a thin layer of coloured foreign material to all or part of a gemstone’s surface, with the intent of either masking the underlying body colour or enhancing a desirable colour. Most often, this coating is applied to the pavilion and/or girdle of the diamond; the way that light refracts as it passes through a diamond creates the illusion of uniform colour distribution.
The durability of diamond coatings vary considerably, depending on materials used and methods of coating applied. Original coating techniques date far back in history when a simple paint or ink was applied to the girdle of a diamond, easily removed by rubbing with a solvent. Most recent advances in technology employ a very thin optical or chemical film which is more durable, but still readily worn away by heat, scratching, abrasion, polishing, and just everyday wear.
In terms of detection, coated diamonds are identified without much difficulty by a trained gemologist in a laboratory.
Irradiation is the process of exposing diamonds to various types of high-energy particles in a nuclear reactor, which slam into the diamond and become embedded in its matrix, in order to change their colour. Irradiation with these high-energy particles alters the internal atomic structure of the diamond, and produces ‘colour centers’. Colour centers are electronic defects in the diamond’s crystal structure, which change the way a diamond absorbs light and therefore its colour. During the irradiation process, diamonds are bombarded with gamma rays, neutrons, protons, deuterons, or electrons.
The effects of these different methods of irradiating a diamond vary; each process produces a different kind of radiation, with different energies and degrees of penetration through a diamond. In other words, the resulting colour depends on the type of irradiation selected and the length of exposure time. Most often, irradiated diamonds are subsequently annealed to further modify their colour into the desired hue, a process described in the following section.
Irradiated diamonds are very difficult to identify using standard gemological equipment; advanced testing by a recognised laboratory is thus imperative.
Annealing is the process of slow heating diamonds at moderate temperatures to deepen, or further alter, the colour of a diamond most often after irradiation. Annealing will frequently enhance a coloured diamond to brighter shades of yellow, orange, or pink. The resulting colours are dependent on the original diamond’s composition, temperature and length of annealing process.
The High Pressure High Temperature colour treatment of diamonds is a process that simulates the conditions a diamond undergoes as the diamond is created deep beneath the surface of the earth.
By subjecting a diamond to extremely high temperatures, under extremely high pressure, HPHT treatment alters the internal atomic structure of the diamond and thus changes the way the diamond absorbs light; in other words, it changes the colour of the diamond.
In terms of identification, HPHT colour treated diamonds may on rare occasions contain visual indicators under magnification, but generally speaking these indicators are not enough to establish the diamond’s correct status – definitive identification of HPHT treated diamonds requires testing with advanced equipment.