What does a diamond look like in ultraviolet light?

A diamond is a cut natural diamond of various types with polished edges and intended for use both in jewelry and in loose form. Using cutting and polishing technology, a natural mineral is transformed into a gemstone with a magnificent play of light. Natural diamonds were first cut by Louis de Bernel in 1454 for the Duke of Burgundy, Charles the Bold. Then the crystal received a round shape and 58 faces. Today, diamond is the most popular gemstone. In 2021, the average cost of a 1-carat diamond is $8. The price of a stone is influenced by four main characteristics: clarity, color, cut and carat weight. And pricing in the diamond market depends on a number of factors. The high price and stable demand for diamonds provoke the emergence of imitations (counterfeits), which are sold under the guise of natural diamonds. Imitation diamonds are natural minerals or artificially grown compounds that are similar to diamond in some properties, primarily visually, but differ from diamond in chemical composition and a number of other properties. The most common are eight types of imitation natural diamonds: cubic zirconia, moissanite, colorless sapphires, white topazes and beryls, spinel, garnet, zircon, rhinestones (glass). The stones that are used to imitate a diamond are cut into both classic round and fancy cuts. Cubic zirconia is a synthetic stone named after the Physical Institute of the USSR Academy of Sciences. Moissanite is a natural or artificially grown mineral. Natural moissanites are extremely rare, so artificially grown stones are used as diamond imitation. Colorless sapphires are gemstones, while white topaz, beryl and spinel are semi-precious natural stones. Colorless types of stones are used as imitation. Colorless garnet and zircon are natural minerals that, like moissanite, are rare. Synthetic types of garnet and zircon are used as imitation. In addition, artificially grown (synthetic) diamonds are used as counterfeits. Such diamonds are cut into round and fancy cuts and are passed off as diamonds. The chemical properties of natural and synthetic diamond are identical. Some jewelry brands use synthetic diamonds to create jewelry. The characteristics of the diamond will be determined by an expert gemologist. The Emporium Gold company in Moscow specializes in the evaluation, purchase and sale of diamonds. In our salon at st. Bolshaya Dmitrovka, 32, a certified expert will evaluate the diamonds and offer a ransom amount within 5 minutes. Ten ways to self-test a diamond are based on the diamond’s exceptional qualities: hardness, density, light refraction and splitting, and chemical properties. It is better to compare the research results with a diamond, the natural origin of which has already been established and confirmed by a gemologist.

Five simple ways to check a diamond:

1. 1. Visual inspection. A natural diamond sparkles not only from above, but from all sides. The stone has no damage, scratches or chips. The diamond’s edges are clear with sharp corners.
2. 2. Frame and brand. For natural diamonds, the setting is chosen from precious metals: gold or platinum. Check for the presence of a hallmark on the metal. The natural diamond is well set in the setting. World-famous jewelry brands use natural diamonds in their products, purchased from diamond mining companies or at prestigious auctions and meeting the requirements of the Kimberley Process.
3. 3. Breath check. The thermal conductivity of natural diamond is six times higher than that of copper or silver. And in comparison with mineral glass with a thermal conductivity of 1 W/(mK), the thermal conductivity of diamond is 2100 W/(mK). If you breathe on a natural diamond, the fog subsides within 1-2 seconds.
4. 4. Water test. Contrary to the myth about the ability of a diamond to become invisible in water, a natural diamond in water will remain visible because. The refractive index of diamond is 1,8 times higher than the refractive index of water. A drop of water on the surface of a natural diamond will not spread and will retain its original shape due to the difference in the density of water and diamond: 1,0 g/cm 3 versus 3,5 g/cm 3 .
5. 5. Text verification. Due to the high refractive index of light through a natural diamond, it is impossible to read the inscription on paper or text. Light entering the crystal is instantly reflected from the edges, and the inscription under the diamond will be indistinguishable.

Five difficult and dangerous ways to test a diamond:

1. 1. Glow under ultraviolet light. In ultraviolet light, a true diamond will glow blue. However, some natural diamonds of the highest quality and clarity may fail this test. Such diamonds are an exception.
2. 2. Heating. The melting point of diamond is 3700-4000 °C at a pressure of 11 GPa. If a diamond is heated over a fire, the natural mineral will remain unchanged. And, for example, synthetic moissanite will acquire a green tint, which will not disappear after cooling.
3. 3. Glow color. Place the diamond on a white piece of paper. Shine it from above, for example, with a flashlight so that the light reflected from the stone passes onto the paper. The reflections of a natural diamond will look like the flame of a gas stove burner without the bright rainbow tints.
4. 4. The diamond is not visible on the x-ray. The carbon that makes up a diamond does not block the rays of an X-ray machine. In the photo, the stone will look like a uniform, blurry spot.
5. 5. Presence of defects. Diamond is a natural mineral that can have defects. For example, small inclusions, cracks, structural defects and twin seams. If a diamond is of perfect clarity, it means that the crystal is either artificially grown, or it is a diamond of the highest quality, the cost of which is calculated in five figures in dollars and increases with the weight of the stone. For example, 1 carat of the highest quality natural diamond (D color, IF clarity) according to the Rapaport Diamond Report price list in March 2021 is 16,7 thousand dollars.

The presence of defects in a stone is one of the signals about the natural origin of a diamond, because today technology already makes it possible to imitate natural defects in a crystal. To confirm the authenticity of a diamond, you must contact one of the accredited gemological laboratories.

Certification of diamonds in Russia is carried out by laboratories that have been registered (accredited) with Rosstandart and the Assay Inspectorate. International gemological laboratories: Gemological Institute of America (GIA), American Gemological Society (AGS), Higher Diamond Council (HRD), International Gemological Institute (IGI), European Gemological Laboratory USA (EGL USA), European Gemological Laboratory (EGL), Gemological Center (GCI-inc).

The ten self-verification methods listed do not guarantee the authenticity of a diamond. Only a certificate from an accredited gemological laboratory will dispel doubts and determine the true value of a diamond.

Almost all minerals, which include diamonds, react to ultraviolet light, namely they fluoresce – they emit light that is not visible to humans in normal daylight, but becomes noticeable in UV rays. This effect is used to solve various problems, including searching for diamonds, analyzing their purity and composition, determining the value of stones and checking their authenticity.

Why do diamonds fluoresce under UV light?

The ability of diamonds to luminesce when exposed to ultraviolet light is caused by two factors:

• defects in the diamond crystal lattice;
• the presence of impurities in the structure of the stone – chemical substances with incomplete electron shells of atoms (the so-called luminogen elements).

However, if we answer the question of whether diamonds glow in ultraviolet light, it should be noted that the purest (highest quality) diamonds do not fluoresce in UV rays, which is due to the uniformity of their composition and the absence of defects at the molecular level.

Fluorescence and luminescence of diamonds

If we do not take into account pure diamonds, for which fluorescence is not characteristic, depending on various factors, for example, the level of transparency of the mineral, the conditions of its formation, the presence of inclusions of certain substances and other conditions, diamonds can fluoresce in different ways: from the most common pale blue (transparent stones) to green and yellow (opaque brown diamonds).

The color group of fluorescent diamonds is determined by the primary color observed when the mineral is exposed to UV rays. In world practice, fluorescence is divided into four categories: from zero to strong. In addition, some diamonds can stand out in a separate group with a very strong glow. An interesting fact is that the fluorescence of diamonds has a completely different effect on their value in different markets around the world. So, if in the countries of North America stones that glow in UV light are more expensive, then in Europe everything is exactly the opposite. As for the domestic market, fluorescence has virtually no effect on the cost of both the stones themselves and jewelry with them.

The second interesting fact is that diamonds continue to glow even after the ultraviolet light source is turned off. Thanks to this effect, you can distinguish a fake from a real or synthetic stone.

Checking diamonds for authenticity

How to easily distinguish a real diamond from a synthetic one or cubic zirconia/glass can be seen in the video below.

In a nutshell, natural diamonds continue to glow on their own for quite a long time after ultraviolet flashlight switched off.

In order to see the glow of a diamond in UV rays, it is suitable ultraviolet flashlight or lamp with a wavelength of 365 nanometers or 395 nanometers, but always with a black filter! The second option works better, but is also more expensive. At the same time, when choosing a homologous UV flashlight, it is worth remembering that the higher the power of the UV flashlight, the higher its efficiency.

In general, ultraviolet light can be used to search for precious stones, as well as by pawnshop employees, diamond sorters, appraisers, sellers, and other specialists whose professional activities are related to diamonds.