Tips for stone care

How to distinguish a natural diamond from an artificial one?

Unlike a diamond that plays with its facets, a natural diamond does not look as presentable. The jeweler receives a nondescript-looking sample with an irregular shape for processing. The mineral is dull, its surface is covered with a kind of “crust”, riddled with cracks. But even in this state, the diamond is already able to reflect light and play with its edges. The jeweler’s task is to cut the stone so that its individual features in the form of voids and cracks become its additional advantages. A diamond in its natural form will be of interest to collectors and people who want to receive an exclusively cut diamond. For an ordinary person, it is possible to purchase a diamond when traveling on “diamond tours”, where stones are purchased directly at mining sites. In order to avoid becoming a victim of deception or to correctly evaluate a specimen that has fallen into your hands, it is worth understanding the signs of a genuine diamond.

Characteristics of the stone

  • The chemical formula of diamond is C (carbon).
  • The variance is 0,63.
  • The refraction of a shining crystal is 2,4175, the indicator can change upward due to the inclusion of impurities.
  • Hardness on the Mohs scale is 10 units.
  • Specific gravity – 3,48-3,55 g/cm3.
  • The mineral is resistant to acids and alkalis.

Types and differences of analogues

Due to the high cost of diamonds, jewelers and manufacturers of electronics and equipment are looking for ways to reduce production costs without sacrificing quality. This is how diamond analogues appeared, making it possible to imitate the shine, hardness and aesthetic component of natural stone.

  • Moissanite is a silicon carbide. In terms of its ability to sparkle, moissanite is even 25% ahead of diamond. The stone also refracts colors perfectly and has similar thermal conductivity. Moissanite is inferior only in hardness – 9,25 on the Mohs scale.
  • Cubic zirconia or cubic zirconium. Its low cost made it an ideal option for inexpensive jewelry products. The characteristics are significantly inferior to diamond and moissanite.

Also, rhinestones (the cheapest glass option), colorless sapphires, rutile, fabulite, yttrium-aluminum garnet, gallium-gadolinium garnet, zircon, and scheelite can be used as substitutes.

In most cases, the desire to confirm the authenticity of a stone applies to diamonds. When purchasing a product or inheriting jewelry, you want to understand how valuable the purchase is. A diamond is a cut diamond, their properties will be identical, except for trying to see the text through the stone. The cut will prevent you from seeing anything through the stone due to the refraction of light within. Other verification methods are suitable in both cases.

Ways to check

Not only diamond is colorless and transparent. There are other stones with similar characteristics. To understand that what you have in front of you is a specimen of a diamond, you can use both everyday verification methods and expert evaluation options. The ideal option is a comparison with a standard, but either jewelers and collectors or gemological laboratories can afford this. In other cases, it is worth relying on knowledge about the qualities of diamond and its physical and chemical properties. Visual inspection and hardware testing in the laboratory are also possible.

Natural qualities

Diamond has a unique intensity of shine; it sparkles brightly, regardless of the type of light source. The stone has ideal transparency, but to come across an absolutely colorless mineral is a great success.

The shade of a diamond depends on the concentration of impurities, inclusions, as well as the intensity of exposure to radiation. One stone can have several shades at once. Most often in nature, stones of white and yellowish colors are found.

Gray milky and black color is a sign of a technical diamond. The board, ballas and carbonado units are also painted. Of all mined diamonds, aggregates account for 80% of the total volume.

It is impossible to find two identical diamond samples in nature; stones are as unique as fingerprints.

Hardness

Diamond has the highest rating on the Mohs scale. This is the hardest material. Diamond has the highest abrasion resistance. This is the reason for testing the stone with sharp objects and abrasives. A diamond can only be scratched with the same stone. Natural diamond can cut glass.

But the proposal to hit the diamond with a heavy hand may turn out to be dubious. In different directions of the crystal, its hardness varies. If you hit it too hard, the diamond will split along planes parallel to the edges of a regular octahedron. The technology of cutting, grinding and cutting rough diamonds is based on this property.

If you do not plan to cut the fragments in the future, it is better to move the hammer away from the stone.

Thermal conductivity

A diamond can be verified for authenticity by its characteristic feature of thermal conductivity. It is suggested to breathe on the sample: if the stone is real, then there will be no condensation from breathing on it. Also, it will take a long time to warm a diamond in your hands. It is worth remembering that you can only distinguish a diamond from a glass fake or a synthetic analogue. If you hold a natural gem with a colorless color, it may have characteristics similar to a diamond.

The thermal conductivity of diamond is 0,9-2,3 kW/(m*K), this is the highest among known solids. That is why it is used as a semiconductor. The efficiency threshold of silicon analogues cannot exceed 100 o C.

Due to the high thermal conductivity of diamond, for example, weapons cool quickly. The thermal conductivity of diamond [0 35 cal / (cm-sec – C)] is higher than the thermal conductivity of hard alloys [0 05 – 0 19 cal / (cm-sec – C) 1 and high-speed steel [0 05 – 0 07 cal / (cm-sec — C) 1. This property allows heat to be removed from the cutter in a diamond tool faster than in a carbide tool.

Fat absorption

This property of diamonds is used, among other things, when raw materials are supplied for processing. Diamonds stick if you first drop regular vegetable oil on them and then press them to the surface of the glass. Counterfeits and other minerals do not react this way, so the method is considered 100%.

Another option for checking the authenticity of a stone is to use a felt-tip pen with thick ink. If you draw a line across the surface of a fake, the ink will fall out in drops, but on a real diamond the line will be smooth.

Interaction with different environments

A diamond is visible in water, it will not disappear. The density of water is less than that of a diamond; the refractive index of light will also be inferior to a gem.

  • Density: 0,10 g/cm³ for water versus 3,47 – 3,55 g/cm³ for diamond.
  • Light refractive index: 1,33(H2O) and 2,42 (diamond).

Based on the numbers, it can be seen that hiding a stone in a bottle or glass of water will be problematic in reality. But water can establish the authenticity of a stone. If you drop water on it and try to puncture the drop, it will remain intact, but with fakes it will spread.

Dust will also help to reveal a fake diamond. If you place a stone near small particles, the dust will be attracted to the fake, but the real diamond will remain clean.

Under the influence of high temperatures of 800-1000 o C, diamond can return to the graphite state. That is why they must be stored in a fireproof safe or in a safe deposit box. Vacuum storage will help increase the critical interval to 2000 o C.

Diamond is inert towards solutions of acids and alkalis, but is quite easily etched at 600-800°C in molten alkalis, salts of oxygen acids and metals. But if you put a fake in hydrochloric acid, it can change color, turn brown or dissolve.

If you run aluminum over a ground sample, a “graphite” trace will remain on the diamond. Important: such a mark is difficult to remove later, so it is better to experiment on an inconspicuous area.

visual

If it is not possible to obtain the opinion of an expert gemologist, then it is worth using a magnifying glass with X10 magnification or a microscope. It is ideal if you have a guaranteed genuine diamond as a standard for comparison.

  1. Natural stone will always have small defects – cracks, inclusions. Flawless stones are very expensive. In a diamond with an average or “democratic” price, the absence of “imperfections” should be alarming.
  2. Diamond’s ability to reflect light and sparkle is present even in rough stones. A true diamond, when processed, sparkles on all sides, not just on the edges.
  3. Clear and even edges are another visual sign of a genuine stone. Even if it was worn for a very long time, the edges will not be erased. The girdle of the diamond is rough and matte, the smooth and transparent girdle is the privilege of the “glasses”.

To check the quality of a stone “by eye” requires good practical experience. If you don’t have one, it’s wise to enlist the help of a professional appraiser or jeweler who is not an interested party.

Using instruments

Electronic diamond testers are used to determine the authenticity of diamonds. These are devices that focus on the thermal conductivity and reflective properties of stone. It is noteworthy that such a tester will identify a true diamond not only among glass imitations. Natural stone can be found even among artificial analogues.

If the tester model relies only on the thermal conductivity indicator, then it is possible to “deceive” it. Artificial mussanite will have the same value as the original. Will give double hardness. On the Moss scale, moussanite is inferior to diamond in hardness by 0,75 points.

A tester based on light refraction will help you weed out even high-quality imitations. Mussanite will have higher values ​​than diamond. However, such testers have a weak side – they only work with cut stones.

The best option is combined testers. The American brand “Gemoro” is popular among both individual entrepreneurs and owners of jewelry chains. Its cost is about 7000 rubles. There are also Chinese pocket analogs – their cost is 10 times less, they are bought by private individuals. Purchasing a diamond tester is important for those who regularly purchase jewelry, including from collectors and individuals.

You can also check the authenticity of a diamond using laboratory instruments:

  • Under X-ray radiation, the diamond will glow a rich green color;
  • UV light (quartz lamp) will cause the diamond to glow yellowish, violet, pink and blue.

You will not see white reflections in the case of a genuine stone.

It is important to remember that radioactive plating can be used to give a diamond a fancy coloring. At the same time, it is impossible to determine whether the stone was “ennobled” outside a gemological laboratory.

Today we can confidently state the fact that synthetic diamonds have ceased to be a laboratory rarity and have entered the market as an alternative to natural diamonds. Therefore, we hasten to tell you about modern methods for identifying artificially grown gem-quality diamonds.

Thanks to active contextual advertising of online stores presenting moissanites as a “synthetic analogue of diamonds,” some of our clients mistakenly attribute synthetic diamonds to imitation diamonds, but this is completely wrong. Imitations such as cubic zirconia and moissanites, which only look similar to diamonds, actually have completely different chemical and physical properties from diamonds and are easily recognized by gemologists without any tools. In the case of laboratory-grown diamonds, everything is much more complicated.

A wide range of colors of natural (including modified) and synthetic diamonds are available on the market. Because these diamonds vary widely in value, accurate identification is of utmost importance to jewelry buyers.

In rare cases, an expert can recognize that a diamond is man-made using standard gem testing equipment. But at the moment, to accurately identify the origin of a diamond, it is necessary to use advanced scientific tools. The leader in the field of diamond diagnostics is traditionally the GIA laboratory, which has created an extensive database on the gemological properties of diamonds.

Classification of diamonds by type

Beginning in the 30s, scientists began to note common features of some diamonds. Based on differences in clarity when exposed to ultraviolet light, they grouped diamonds into two main categories, today called Type I and Type II. In 1959, they discovered that nitrogen atoms are the main chemical impurity in diamonds, but unlike Type I diamonds, Type II diamonds do not contain it.

This diagram shows a simplified version of the diamond type classification system. Type I (top row) and Type II (bottom row) diamonds can be divided into two subcategories based on the arrangement of carbon atoms (and impurities) in the diamond’s structure. C = carbon atom, N = nitrogen atom and B = boron atom. The type of diamond can be quickly determined using infrared spectroscopy.

The vast majority of natural diamonds are Type Ia. This type of diamond contains many nitrogen atoms arranged in clusters or pairs. This type of diamond cannot be grown artificially. Type Ib diamonds contain scattered or isolated nitrogen atoms that are not found in pairs or clusters. Type IIa diamonds contain almost no nitrogen, while type IIb diamonds contain boron. Diamonds of the last three types are extremely rare in nature, but in turn can be grown in the laboratory.

In gemological laboratories, type I and type II diamonds are distinguished by differences in transparency under short-wave ultraviolet radiation. However, final separation will require the use of infrared spectroscopy, a technology available only to large scientific centers.

Diamond Type (Color) Natural HPHT synthetic CVD synthetic
Ia (colorless) Often
Ib (yellow) Rarely Attention! Rarely
IIa (colorless) Rarely Attention! Attention!
IIb (blue) Rarely Rarely Rarely

This table illustrates the prevalence of natural and cultured diamonds of different types. Most synthetic diamonds are either Type Ib or Type IIa.

How does a diamond grow?

Crystals of natural diamonds were formed millions and sometimes billions of years ago deep in the bowels of our planet (more than 160 km). Much later they rose to the surface as a result of volcanic eruptions. These eruptions created narrow vertical tubes of igneous rock called kimberlite. The diamond content in kimberlite pipes is negligible – on average, to find a diamond weighing 1 carat, it is necessary to process 200 tons of ore.

Natural diamond crystals (right) have typical rounded octagonal shapes, which are a result of the forces acting on the diamond deep within the earth. They are brought to the surface by volcanic eruptions, forming kimberlite pipes (center). The ideal crystalline form of natural diamond is an octahedron (left). Diamond growth occurs along all eight faces of the crystal.

Diamond is born in a certain range of temperature and pressure. In nature, diamonds were formed at higher temperatures than those grown by humans today. At high temperatures in the natural environment, diamond crystals form in the form of an octahedron (two pyramids connected by the bases). In laboratory conditions, where it is not possible to create a similar temperature, the structure of the grown crystals will have a cubic shape. Inside a natural diamond, nitrogen atoms are grouped into pairs or clusters over millions of years, which is why most natural diamonds (more than 95%) are Type Ia.

Synthetic diamonds are grown for a very short time – from a few weeks to a few months, under conditions different from the formation of natural diamonds, so the crystal shape of a synthetic diamond differs from the shape of a natural diamond, but only before the diamond is cut into a diamond.

Diamond synthesis technologies

The first man-made diamond was produced in the mid-1950s in the form of tiny crystals. It took 40 years to grow large diamond crystals suitable for use in jewelry. Improvement of diamond growing technology continues to this day, and every year more and more companies are involved in this process. Following De Beers, almost all the major players in the jewelry diamond market opened their own divisions for the production and cutting of synthetic diamonds. The vast majority of man-made diamond production capacity today is concentrated in China.

The traditional method of diamond synthesis, called high pressure high temperature (HPHT) growth, involves forming a diamond crystal from a molten metal alloy such as iron (Fe), nickel (Ni) or cobalt (Co). A more modern method is called CVD – chemical deposition of carbon atoms from the vapor phase in a vacuum chamber or growth at low pressure and high temperature (LPHT). In both methods, a diamond crystal or plate is used to initiate growth.

Synthesis of HPHT

In HPHT technology, the diamond is grown in a small capsule in which very high pressure is created. Inside the capsule, the starting material of diamond powder is dissolved by the molten metal flux and then crystallized on the seed to form a synthetic diamond crystal. A diamond is synthesized from several weeks to a month or more.

HPHT synthetic diamond crystals typically have cubic facets in addition to octahedral ones. Since the crystal shapes of natural diamond and HPHT-grown diamond are different, their internal growth patterns are also different, which serves as one of the most reliable ways to diagnose such diamonds.

The resulting synthetic HPHT diamonds often exhibit visual characteristics such as uneven color distribution, fluorescence zoning, and grain patterns associated with the cross-shaped structure of the initial seed. Accidental inclusions of dark metallic flux (possibly weak magnetic properties) are also very common. In some cases, the diamond exhibits persistent phosphorescence after the ultraviolet lamp is turned off. These synthetic diamonds can be identified using laboratory techniques such as spectroscopy.

Most HPHT grown diamonds are yellow, orange-yellow, or brownish-yellow in color. Almost all of them are type Ib, which is rarely found in natural diamonds.

Creating colorless diamonds using HPHT technology is not a trivial task, since inhibitors are needed that can remove nitrogen atoms from the growing diamond crystal. In addition, the growth rate of colorless diamond (Type IIa or weak Type IIb) with acceptable purity is lower than that of synthetic Type Ib diamond, requiring longer growth times and greater control of temperature and pressure parameters. Today, these problems have been solved and the latest generation installations make it possible to grow colorless or blue crystals for diamonds over 10 carats.

Adding boron to the growth system results in blue crystals. Other colors, such as pink or red, can be obtained by irradiating or heating already grown diamonds.

In HPHT synthesis, the press (left) applies extremely high pressure and temperature to the center of the growth chamber. This allows synthetic diamond crystals to be produced from combinations of cubic and octahedral facets (center and right).

CVD synthesis

CVD technology involves the growth of diamond inside a vacuum chamber filled with a gas containing carbon, such as methane. Using a laser, gas molecules are destroyed and carbon atoms are deposited onto prepared seed plates. Crystallization takes several weeks, with several diamonds grown at the same time. The exact amount depends on the size of the chamber and the number of cells in which growth occurs. Synthesized diamonds often have graphite on their outer surfaces and a brown color that is removed by heat treatment before being cut into a diamond.

Most CVD diamonds have brown or grayish tints, but if small amounts of nitrogen or boron are used in the synthesis, yellow, pink-orange, or blue crystals may form. Colorless diamonds are easier to produce using this method, but take longer to grow. Currently, it is believed that the majority of colorless diamonds grown using CVD technology are brown diamonds decolorized using HPHT technology. CVD diamonds are most often Type IIa and also have different hematological properties than HTHP diamonds. They are more transparent, exhibit more uniform coloration (if shade or fancy color is maintained), and have their own “striped” pattern when viewed through crossed polarizing filters. CVD diamonds are also characterized by microscopic inclusions of graphite.

In CVD synthesis, synthetic diamond growth occurs by depositing carbon-rich gas onto a flat seed plate. Synthetic diamond grows in thin layers, and its final thickness depends on the amount of time allowed to grow (left). This results in flat, tabular crystals (center and right) coated on the outside with black graphite crystals.

Like HPHT, CVD technology continues to improve, offering consumers larger sizes and better purity characteristics. Today, there are diamonds grown using CVD technology and weighing more than 4 carats.

Example crystals (from left to right): natural, synthetic HTPH and synthetic CVD. The octagonal faces are shown in yellow and the cubic faces in blue. Most natural diamonds grow as octahedra (left), but HPHT synthetics (center) typically show a combination of cubic and octahedral facets. Octahedral facets are completely absent from HTHP-grown synthetics (right). The directions of crystal growth are shown by arrows. The dotted lines indicate the position of the seed crystals during the HPHT synthesis process and the edges of the CVD diamond crystal.

Identification of synthetic diamonds

Over the past 10 years, a large number of companies have appeared in the market for laboratory synthesis of gem-quality diamonds. They are continually improving the clarity, color, and weight of the diamonds they produce. Despite this, leading laboratories such as the International Gemological Institute (IGI) and the Gemological Institute of America (GIA) rarely encounter synthetic diamonds, mostly unknowingly being shipped as natural diamonds. A good indicator of the rarity of synthetic diamonds is the fact that a specialized certificate for grown diamonds was introduced by the largest GIA laboratory only in 2019. The IGI laboratory was a pioneer, offering a separate certificate for synthetic diamonds much earlier than the GIA. That’s why most man-made diamonds on the market today are IGI certified.

Identifying the origin of a diamond requires several pieces of equipment, including a refractometer, an ultraviolet lamp, a binocular microscope, a polariscope, and some additional testing tools that can cost hundreds of thousands of dollars, as synthetic diamonds continue to improve in quality and become increasingly difficult to distinguish from natural diamonds. .

HTHP Diamonds Diamonds CVD
Uneven color distribution Even color distribution
Grain Pattern No grain pattern
Unusual fluorescence color Unusual fluorescence color
Rarely phosphorescence Rarely phosphorescence
Inclusions in the form of metallic flux Sometimes inclusions in the form of dark dots
No striped pattern “Striped” pattern

This table presents the visual features of two types of synthetic diamonds.

Colored synthetic diamonds grown using HTHP technology often have uneven coloration, which can be seen under a microscope and, if necessary, by immersing the cut stone in water or mineral oil to minimize surface reflections. This color zoning is caused by the way impurities such as nitrogen become integrated into the diamond crystal as it grows. Sometimes natural diamonds also exhibit color zoning, but it differs from the geometrically ideal pattern of HPHT diamonds.

Color unevenness in HPHT colored diamonds is associated with differences in the facets of the crystal and, as a result, patterns different from those observed in natural diamond crystals. Certain impurities are concentrated in the corresponding growth directions. Regions labeled type Ib contain dispersed impurities of nitrogen atoms, regions labeled IIb contain boron, and colorless regions (type IIa) are generally free of impurities. Only synthetic diamonds typically exhibit a combination of nitrogen and boron atoms in the same crystal.

CVD diamonds, on the other hand, typically exhibit an even distribution of color throughout the crystal.

Lab-produced HPHT diamonds often contain opaque black inclusions of hardened metal that have a characteristic sheen. Diamonds with such inclusions can have magnetic properties. Diamonds grown using CVD technology do not have metallic inclusions, although they may contain inclusions of graphite or some other mineral.

Synthetic HPHT diamonds often contain metallic flux inclusions that appear black and opaque when held up to light, but have a metallic luster when caught in the glare. In some cases, an HTHP diamond will exhibit magnetic properties due to the presence of numerous nickel-iron (Ni-Fe) flux inclusions.

When viewing a natural diamond between two polarizing filters oriented at 90 degrees to each other, the diamond often displays a striking cross-hatching or mosaic pattern of color interference (distortion). This interference occurs as a result of pressure applied to the crystal while it was deep on the Earth’s surface or while it was being extracted to the surface by an eruption. Unlike natural diamonds, synthetic diamonds grow in an environment of almost uniform pressure; they are not subjected to extreme loads and therefore do not show any deformation pattern.

The fluorescence of synthetic diamonds is also very useful for identification – it is often stronger in short-wave than in long-wave ultraviolet, and has a characteristic pattern (figure).

HPHT synthetics typically exhibit a cross-shaped fluorescence pattern when viewed through a pavilion or crown.

HPHT grown diamonds tend to exhibit a cross-shaped fluorescence pattern on the crown or pavilion of an organic diamond. Diamonds synthesized using CVD technology may have a striped pattern when viewed through the pavilion facets. Typical fluorescence colors are green, yellow-green, yellow, orange or red. When the UV lamp is turned off, synthetic diamonds may phosphorescent (glow) for more than a minute.

The GIA laboratory uses the DiamondView instrument to visualize the fluorescence of the diamonds being tested, thereby revealing the characteristic patterns of diamond crystal growth. Unfortunately, the cost of this device does not allow its use in domestic laboratories.

DiamondView (above) allows an expert to view the growth patterns of natural and synthetic diamonds. The concentric growth pattern (right) identifies this stone as natural, while the cross pattern (center) is an indication of synthetic HTHP. The regular bands visible in the center of this round diamond (left) indicate that it is a CVD-grown diamond.

A real challenge for the jewelry industry is the inspection of small diamonds, batches of which are often a mixture of thousands of natural and synthetic diamonds. Today, rapid testing of small diamonds, carried out by GIA experts using a specially designed automatic installation, is extremely popular at foreign exhibitions.

Today, the production of synthetic diamonds is so popular that the GIA laboratory has acquired its own equipment for growing and subsequent research of diamonds using CVD technology.

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