Laser drilling : is an important treatment aimed at improving the clarity of the diamond (photo on the right). This results in straight laser drill holes that are easy to identify under magnification. Drill holes typically have a round cross section, while natural channels, which also extend inward from the surface of the diamond, are square, triangular, or hexagonal. Some treaters use a different laser technique that opens or widens a cleavage and helps to reach and whiten dark inclusions near the surface. The resulting feather (called ILD) looks more natural than a traditional laser drillhole. To identify this treatment, a microscope and various lighting techniques are used.
Fracture filling : is another treatment that improves clarity, and the flash effect is one way to detect it. To look for the flash effect, you need to use the magnification and reflected light to find where the fracture hits the surface. We then switch to lighting on a black background and visualize the presumed fracture filled in parallel to the fracture plane. We rock the stone repeatedly so that the background changes from light to dark. If the fracture is filled, two colors are visible and "blink". The effect occurs because the refractive index of the filler glass does not exactly match the refractive index of diamond for all wavelengths of light. Besides the flash effect, we can also see a cracked texture on the surface of the fill glass and gas bubbles trapped inside.
HPHT treatment : Treaters can remove the brown color from some diamonds through a treatment that combines high pressure and high temperature (HPHT). One of the effects of this treatment is the formation of graphite around the mineral inclusions. This is called graphitization. The cleavages of some HPHT treated diamonds appear glassy on the inside but grainy near the surface. Outward radiating stress cracks sometimes surround solid inclusions. HPHT treatment is most often used to make diamonds colorless. Most HPHT treated diamonds show no visible signs of treatment. The detection of this treatment often requires advanced tests in a gemological laboratory recognized as the GIA.
Irradiation : This is a brief exposure to electrons, neutrons, gamma rays, or a combination of both in a nuclear reactor. This treatment turns natural diamonds green and synthetic ones turn light yellow. Subsequent controlled heat treatment (annealing) changes the green to brownish orange. Sometimes this results in blue, orange and very rarely pink, purple or red colors. Unfortunately, it is difficult to predict which color will be processed each time. All green diamonds get their color from radiation exposure, but radiation can be natural or created in the laboratory. In many cases, even with sophisticated laboratory equipment and techniques, it is not possible to naturally separate natural green diamonds from processed green diamonds. An extremely dark green diamond color can be created by long exposure to radiation in a nuclear reactor. If you come across a diamond that is so dark green that it looks black, you can be pretty sure that it has been irradiated. Almost all naturally black diamonds are in fact extremely dark gray.
Since diamonds are generally more valuable than other stones, it is very important that any treatment, including irradiation, is detected and disclosed. This makes the testing process much more complex and time consuming. Most original diamond color testing should be done by a gemological lab. Spectrum testing is a way for a laboratory to detect radiation treatment. When cooled to extremely low temperatures, irradiated and annealed diamond can exhibit a spectrum with a thin line around 594 nm. Achieving sufficiently low temperatures requires the use of liquid nitrogen, which is why this test is usually performed in the laboratory. Before refining irradiation techniques, diamonds were bombarded with subatomic particles in a cyclotron. On these stones, magnification revealed low penetration and intense color zoning around the culet. Irradiation of a round gloss produces an umbrella-shaped pattern. Irradiation from the crown side causes areas of color to duplicate the faceted pattern that appears slightly below the surface. Today's diamond irradiation methods generally leave little or no color zoning. If color zoning is present, it is subtle and difficult to detect. A gemological microscope, diffuse transmitted light, and methylene iodide immersion can help find color zoning associated with irradiation. Natural and synthetic boron colored blue diamonds conduct electricity, while irradiated blue diamonds do not. Tests to separate the two are usually done in a gemological lab. Radioactivity is only detectable in certain irradiated diamonds. The improved irradiation techniques used today leave no measurable radioactivity behind.
Less common diamond simulants are strontium titanate, gadolinium gallium garnet (GGG), yttrium aluminum garnet (YAG), synthetic quartz, and artificial glass.
Strontium titanate : Has a high refractive index and is unirefringent like diamond, but its polished glassy to subadamantine luster, extreme fires, and low thermal conductivity set it apart.
GGGs and YAGs : These synthetic garnets have high refractive indexes and isotropic, their luster is glassy to subadamantine, and both register as non-diamond with a thermal tester, but some differences help you separate them from one another. The fires of the GGG are moderate, while those of the YAGs is weak. GGGs fluorescence is moderate to strong pink orange under shortwave UV, while YAGs are inert to moderate orange under longwave UV and inert to weak orange under shortwave UV. The density of YAGs is 4.50 to 4.60, while that of GGGs is 7.05. YAG's pavilion flash is blue and purple on most facets, while GGG's is orange and blue, but this test only works with well-proportioned round brilliants.
Synthetic quartz : is typically cultivated for use in electronic devices, but some have marketed it as a diamond simulant. Quartz's low refractive index (1.54-1.55) and birefringence make it easy to distinguish from diamond and other colorless materials, but not from its natural counterpart.
Artificial glasses : are unirefringent, and of a lower refractive index than that of diamond (1.47 to 1.70), the vitreous luster and the weak to nonexistent fires prove that it is not a diamond. Magnification can reveal gas bubbles, surface cavities and flow lines (features completely absent from diamond). High lead glass, used in fashion jewelry, has a higher refractive index and more fires than lead free glasses.
Assembled stones that mimic diamond include strontium titanate doublets coupled with colorless synthetic sapphire or synthetic spinel. If a separation plane at or below the belt is present, this is proof that it is assembled. If further tests are inconclusive, it is possible to prove the assembly by finding the differences in refractive index between the crown and the bell.
Some doublets use the diamond as the crown and a diamond simulant as the pavilion. If you only touch the crown with a thermal tester, it will accurately indicate "diamond". To avoid making this mistake, one should use the thermal tester on the horn, then look for a separation plane under magnification or check with a UV lamp to see if the crown and horn fluoresce differently.
Hardness : 10
Density : 3.50 to 3.53
Fracture : Irregular
Streak : White
TP : Transparent to opaque
RI : 2.435
Birefringence : 0
Optical character : None
Pleochroism : None
Fluorescence : Blue, green, orange
Solubility : Insoluble
Magnetism : Diamagnetic
Radioactivity : None