- How to determine the quality of sapphires
- What stones does corundum belong to?
- How to distinguish stone from glass
The color of sapphire is determined visually by gemologists, when compared with reference specimens. It is characterized by a combination of hue, saturation and lightness. The main color tone of the stone is pure spectral blue, acceptable secondary shades are purple and green. Sapphires are also divided into five categories according to lightness and three categories according to color saturation. However, for commercial purposes, a simplified classification of sapphires by color is usually used, which provides for only three groups. The first is bright blue sapphires, the second is mid-blue sapphires, the third is light blue sapphires.
The purity of sapphire is also determined visually, with the naked eye and with a magnifier with a 10x magnification. Four cleanliness groups have been adopted. The first is almost perfectly transparent sapphires without defects or with single small defects, which are noticeable only with a significant increase. The second is transparent stones with a few small defects and natural inclusions that are not visible to the naked eye. The third is sapphires with a partial loss of transparency, with defects and inclusions that are very clearly visible even with the naked eye. Fourth - sapphires with a noticeable or complete loss of transparency, with numerous, clearly distinguishable defects and inclusions (or single defects, but very large).
Sapphire weights are measured in carats (1 carat is 200 mg). Small stones up to 1-2 carats are quite common. Large are considered sapphires from 5 carats. They are very rare. The cost of 1 carat of the weight of such a stone, depending on its color and purity, can reach $ 4,000.
The main methods for cutting sapphires are facet and cabochon. Of the facet cuts, the most common is round, but fantasy ones are also often used: “heart”, “emerald”, “marquise”, “oval” and “pear”. Cabochon is a cutting method in which a stone is given a round or oval shape with a convex polished surface. In this way, sapphires are treated with a significant loss of transparency and a large number of defects. The cabochon cut of opaque sapphires with needle-like inclusions of the rutile mineral (the so-called “star” sapphires) reveals the effect of asterism - the appearance of a star gliding over the surface with 6 or 12 rays.
The quality and price of a stone is greatly influenced by its origin. The highest quality are considered Kashmir sapphires. They have a cornflower blue color and a silky sheen. Since the deposit in Kashmir is no longer being developed, such stones are rare jewelry and are fabulously expensive. Ceylon sapphires, which are characterized by a less saturated light blue color, are also highly valued. Siamese sapphires from Thailand are significantly inferior to them in price. Up to 80% of all sapphires are mined in Australia, but these stones are the cheapest, since they are very dark, with a greenish tint, of a low degree of purity.
Abroad adopted another system for assessing the quality of faceted sapphires proposed by the American Gemological Institute (GIA). The correspondence between the Russian and Western systems is as follows: the first group of purity is VVS (very, very small inclusions), the second is VS (very small, insignificant inclusions), the third is SI (small but noticeable inclusions), the fourth is I (inclusions visible with the naked eye). Keep in mind that natural sapphires, unlike diamonds, are not completely free from defects, so the IF category (clean under a magnifying glass) is unacceptable to them. If the seller offers you IF category sapphire, it is either a fake or artificially grown stone.
How to determine the authenticity of sapphire?
Fake gems are ennobled natural minerals of no value. Under the guise of sapphire they give out tourmaline, cordierite, spinel and other corundums, which are similar in signs to it.
Gold earrings with diamonds and sapphires, SL, gold ring with diamonds and sapphires, SL, (price by reference)
What characteristics should be considered when diagnosing the origin of a stone and determining its natural origin? First of all, on it:
- structure
- transparency,
- color,
- strength,
- cost
- availability of quality certificates.
But if sapphire corundum is already purchased, then it is possible to determine whether it is synthetic or natural, by conducting a gemological examination or at home.
Sapphire structure
Real gemstones do not have a homogeneous structure, a uniform color and interspersed air bubbles, flux or copper. If in a high-quality fake a natural tourmaline stone was used, similar in structure and color to sapphire, it is not possible to visually distinguish a fake from real corundum. In synthetic stones there are always gas bubbles, small inclusions of gold or platinum, color zoning.
Self Stone Authentication
With a visual inspection, you can determine only the color of the gem and its transparency. Real sapphire is rich and uniform in color, resembles silk or velvet. And spinel fakes are darker in color, from tanzanite have a shade of red, and from aquamarine they resemble the color of a sea wave.
Gold pendant with black and white diamonds, sapphires and topazes, SL, (price by reference)
In addition, sapphire has exceptional transparency, with small inclusions and impurities. How to check sapphire at home for transparency? Easily! By directing a direct ray of sunshine onto a stone, you can see a glint in the shape of a six-pointed star.
Tactile sensations from sapphire are important when viewed. Before you check the sapphire for authenticity, hold it in the palm of your hand - a natural stone is always cold and pleasant. And synthetic fakes do not give such a feeling.
Stone strength
The authenticity of natural stone is evidenced by its strength. So, in terms of strength characteristics, sapphire can only be compared with diamond. Due to its high strength, corundum edges will always be even and smooth. And if you don’t be afraid and draw a sharp object over it, then there will be no trace on the surface of the stone.
But no one will give such a manipulation in the store, so before choosing a sapphire, ask the seller for a corundum quality certificate.
When reading the certificate, check if the purity level is specified - IF. If it is, then the stone is clearly a fake - in genuine sapphires this indicator is not determined.
Cost of a sapphire product
Rarity is one of the characteristics of all gems. Pure stones, without defects and impurities, are rarely found in the natural environment, so a sapphire ring or other jewelry made of it sometimes reaches thousands of dollars in value, and minerals of exceptional quality and size can even reach millions! Synthetic stones cost several times less.
The design of the product with sapphire is simple and uncomplicated so as not to interfere with a full-fledged analysis of the quality of the stone.
Why imitate gems
Due to the beauty and high cost of fake sapphires put on stream. Jewelry often imitate using all kinds of materials and methods. Cheating buyers gives scammers additional profits, but nobody wants to become a victim. Below we describe the basic rules for distinguishing natural minerals.
Sapphire is a very strong stone from the group of corundums; in hardness it is only one unit inferior to diamond. Blue is considered the most common color, but fantasy shades are not uncommon in the mineral palette. These are orange, yellow, pink, green specimens. Colorless crystals are called leucosapphires.
There are no red sapphires. Stones with such shades are called rubies. Blue corundums do not differ from others in physical and chemical characteristics. In the article "Properties of sapphire stone and to whom it suits" you can learn more about all the qualities of this type of minerals. This knowledge will help you figure out how to determine the authenticity of sapphire.
Possible imitations
There are a number of methods that allow you to check the authenticity of sapphire even at home, without special appliances and tools. But first, we list all the possible simulations:
- glass,
- sapphire-like blue natural stones,
- doublets
- triplets
- artificially grown crystals.
The first on the list is glass. Often use an ordinary bottle. Such jewelry is much cheaper. If a blue stone is offered at a price lower than $ 200 per carat, then it is clearly unnatural. An external sign of a glass is the presence of bubbles inside, visible to the naked eye. Such a fake immediately heats up in the hand, if you hold it for at least a minute.
Jewelers use special high-density liquid solutions for testing. Sapphire dipped in a container will sink, and most imitations will remain on the surface.
A professional checks with a special device the refractive index of light, which is equal to 1.774 in blue corundum. These methods do not apply to artificially grown crystals.
Natural imitations
A stone similar to blue corundum is cordierite. It is a blue mineral with a greasy sheen. There are transparent varieties, which just act as imitations. In terms of hardness, the stone is inferior to corundum by two units, but for the external resemblance among the people it was even called "water sapphire."
Kyanite is also inferior to corundum in hardness (7 units) and density (3.67 g per cubic cm), but its blue crystals, when well processed, are easily confused with a first-order gem. The same can be said of tanzanite, the color of which is not in vain called sapphire.
It would seem that it makes no sense to give out a noble blue spinel as a sapphire. However, such cases do occur, although at a price the stone is classified as expensive. This mineral differs from corundum in isotropy, and in hardness it is inferior only by one unit. More details in the article “What kind of stone is spinel and what are its properties”.
Blue tourmaline easily imitate real sapphire as if the younger brother of the blue mineral. Transparent and glass-shine stones will allow to distinguish a fake only to an experienced jeweler. The article “Properties and value of tourmaline stone” will help you remember the necessary qualities, and how to distinguish sapphire from a fake will be described below.
We use a refractometer
To determine sapphire among the natural stones listed above, a special device is used - a refractometer. In other ways, it is impossible to notice the difference in physical properties. An exception is tanzanite, upon careful examination of which the eye catches a reddish hue.
To use a refractometer, find out the light refractive index of each of the listed minerals. For convenience, use the table below:
For sapphire, this coefficient ranges from 1.766 to 1.774. When measuring with a device, the readings of the refractive index must be taken into account to the nearest hundredths. If the deviation is greater than or equal to one hundredth, then you have another jewel.
Home methods
Now let’s see how to check sapphire without using special devices. At home, it is possible to identify a fake made of glass. Thanks to the hardness of stone mentioned above, authenticity is easily determined by mechanical action. Try to scratch the decoration on the side of the pavilion with another stone or needle.
The scratch on the blue corundum remains only from a harder diamond or equivalent sapphire with sharp edges. If there is a mark on the tested jewelry, then this is a fake.
If you consider the blue corundum in the light, then when you turn in different directions, a noticeable change in hue. This is a characteristic of the mineral dichroism phenomenon. Seeing inside the longitudinal stripes, you can suspect kyanite. Turbidity inside indicates spinel.
Magnifier will show the whole structure.
Distributed in the world of fakes, the so-called doublets and triplets. These are composite stones, which are made by craftsmen from several layers. Usually there is glass at the bottom, and a piece of real sapphire on top. The seam that results from gluing is clearly visible when viewed through a magnifying glass.
In this way, it is impossible to fake star sapphire. In fake, the star always stands still, and in natural stone it shifts at every turn of the mineral.
The internal structure of the blue crystal will help to see a magnifier with a tenfold increase. There should not be gas bubbles. But the presence of scanty inclusions of foreign materials is a defining sign of the naturalness of the stone.
Differences artificially grown crystals
Synthetic, that is, sapphire grown in the laboratory, is almost impossible to distinguish from natural. The fact is that stones that are obtained artificially fully preserve all the properties of natural minerals. Therefore, it is difficult for even a specialist to draw conclusions about the origin of crystals.
But remember the main signs of natural sapphires - small size and the presence of inclusions. In laboratories, crystals grow very quickly and grown specimens reach tens of kilograms. Nature "works" slowly, its creations are elegant and quite medium-sized - an average of 3-8 carats.
Gemologists to test put the test sample in a solution of monobromonaphthalene. Highlighting a transparent container on the side on a white background allows you to see the growth lines. If they are curved, then we have synthetics. In natural stones, inclusions are straight.
And one more sign. Looking at the stone in the sun, pay attention to the glare. If they are whitish, then you have a natural mineral in your hands. Artificial sapphire glare under an ultraviolet lamp. But the reflections are not white, but green.
Our advice to buy jewelry is always relevant only in trusted stores where you can see a certificate for the goods. Other details on how to distinguish natural sapphire from artificial sapphire can be found in the article “Difference of synthetic artificial sapphires from natural sapphires”.
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