Gemmology Identifying Diamonds Diamond is one of the most important gemstones traded in the world today. Diamond has all properties in the superlative state- best luster, highest hardness, highest thermal conductivity among gems and these properties help in identification and form the basis for some of the tips to check whether the white stone is a diamond.

t is said that Alexander the stone then do so only with a stone case of simulants, the line will Great found a valley full of both holder or tweezer. Never move appear partially or complete. This Idiamonds and poisonous snakes. your fingers through the diamonds, test can be easily carried out on No one could work out how to you would never know how many unset stones; but care must be retrieve the jewels until Alexander diamonds would get stuck to your taken when they are mounted. had the idea of throwing down fingers and fall out. Confusion is possible with raw meat, to which the diamonds old cut diamonds, in which full attached. When eagles flew down Visual Methods advantage of the low critical angle for the meat, Alexander's men just was not taken in cutting. Here, the had to follow them to their nests. It Tilt Test line may appear unnaturally clear or sounds like fantasy but diamonds The high Refractive Index (RI) of transparent for diamonds. The large are attracted to fat, and the story Diamond makes possible a simple culet and the facet edges will be reminded people how to tell real test to distinguish it quickly from immediately apparent to the naked diamonds from fakes. De Beers still simulants with lower RIs. Hold a eye through the table. This results practice Alexander's trick in their brilliant-cut diamond in a pair of from the larger angle of the pavilion South Africa mines today: They tweezers with its table face up, facets, which allow light to escape use "grease tables" and only the horizontal below the eye. Tilt the through the back of the stone. valuable stones stick. stone away from the body and Not all diamonds would give This test is very much valid even observe the table facet. If the the read through test. Therefore be in day-to-day diamonds business. stone is a diamond, the amount of careful of all fancy cut diamonds, Those who do diamond assorting brilliancy coming from the table will Fish-eye stones or diamonds with can vouch for it. Every sorter lifts the be the same. However if this test is shallow pavilion depth. diamond just by touching the stone carried out on brilliant-cut stones As well as stones like Strontium with a finger and the diamond gets of lower RI, such as YAG or paste, Titanate (same RI of 2.41) and lifted due to the slight oily nature the light will appear to empty out Synthetic Moissanite (a DR stone of the human finger, whereas all from the stone. This test can also be with RIs of 2.648-2.691 and Double other white coloured stones simply carried out on mounted stones Refraction (0.043) which may not fall off the finger. Many who do this give that effect. daily don’t know why this happens. Read through Test It’s the property of diamond to get Diamond has a low Critical Breath Test attracted to grease or oily surface. Angle of 24ْ 26’, which means As diamonds have high thermal The human sweat has some oil that a brilliant-cut stone reflects conductivity there is simple test content in it which is responsible for back most of the light entering it. for identifying diamonds from its the diamonds sticking to the finger. It is therefore impossible to look simulants. Because of its high This is also very important for right through a perfect brilliant cut thermal conductivity, diamond those who are starting business in diamond from the table and see feels colder to touch, any other diamonds. One what is below. Except through the gemstones. It is cold to touch and should always culet, if it is large enough, anything becomes warm quickly, when open star sized would be visible. worn. If a loose stone or diamond diamond packet Draw a line on a piece of paper jewellery is left to attain room carefully and and place the stone with its pavilion temperature and then touched, it slowly. If you face up. In case of a diamond the will feel quiet cold. In this test the want to pick up a line will not be seen at all. In the stone to be tested is taken along with a known diamond. When you Even after many years of constant breathe on the clean surface of a wear, cut diamonds preserve their diamond, the mist that is formed, sharp edges and corners, while will clear much faster in case of the most other gemstones become worn diamond than when compared to its and chipped. Most simulants after a simulants. Care should be taken to few years of wear have rounded or ensure that both the stones are at moulded edges between facets. room temperature when the test is taking place. The recent synthetic Gridle Appearance: The moissanite also has a good thermal girdle of a brilliant-cut diamond is conductivity would therefore give different in appearance from that similar reaction. of other stones. It appears sugary or granular, if it is unpolished. In Water Test case of simulants the girdle would Diamond has a very high surface appear smooth and glass-like. The tension, therefore if the table girdle of a diamond has a matt, surface of a diamond is thoroughly waxy appearance, caused by the clean and free of grease, a drop of fracturing process of bruting. It water on the table will remain as is not dull like ground glass, but a globule for a long time, whereas has a shiny wax-like lustre. This is in case of other stones / simulants, ConfirmatoryT est for identifying only Conductivity high enough to fool the globule will spread out in a round brilliant cut (RBC) diamonds. many of the Thermal testers relatively short time, depending on on the market, but it is easily the mineral. Presence of naturals: A distinguished from diamond with 10x natural on the girdle is an indication magnification. Because Synthetic Tests using a 10x lens of diamond. It is the part of the Moissanite is Doubly Refractive Polishing Lines: Diamonds has original skin of the rough diamond (unlike diamond, which is singly directional hardness and therefore left on the stone and usually looks refractive), inclusions and back the polishing lines run in different much brighter than the girdle. A facet junctions will appear doubled. directions on different facets. natural indicates that the cutter has However, since synthetic Moissanite This means that there are no two tried to retain the maximum weight is often faceted with the table adjacent facets having polishing from the rough crystal. A natural perpendicular to the optic axis, you lines in the same direction. In case may show surface markings in the should examine a suspect stone of simulants, the polishing lines form of trigons, cube markings or from multiple angles to check for always run in the same direction parallel lines. Trigons may be seen doubling. Viewing through several on all facets. This is a Confirmatory on the natural, when they are part of bezel facets will usually produce the Test for identifying diamonds. an original octahedral face. This is a best results. Confirmatory Test. Some inclusions that might be Bearding: In the manufacturing Naturals are good proof that seen in Synthetic Moissanite are process of diamond there is the the stone is a diamond, but there is open, not-quite-parallel, tube- bruting process in which two one simulant – Yttrium Aluminate or like channels. They are usually diamonds are rubbed against one Yttrium Aluminium Garnet (YAG, also hexagonal in cross section, and another in order to form the girdle. If called Diamonair) – where similar might be capped by other inclusions. there is a vibration between the two naturals are occasionally left, during These will appear doubled under diamonds (due to careless handling) manufacturing (by Czochralski magnification, unlike the etch then in the polishing diamond it will Method). But its RI of 1.833 is much channels sometimes seen in natural produce hair like feathers / cracks lower than that of diamond. diamond. Other possible inclusions / whiskers running from the girdle are slender white needles, very fine into the stone. This is known as Doubling of Backseats: refractive lines and pinpoints that bearding and it occurs due to the Synthetic Moissanite is the only are sometimes numerous enough to cleavage property of diamonds. diamond simulant with Thermal form clouds.■ —By Jaushree Panjikar

Facet Junctions: Diamonds exhibit sharp, knife-edge like facet JAYSHREE PANJIKAR junctions, due to their highest hardness. When seen under a 10X Pangem Testing Laboratory lens, the edges of the diamond 10 Sangeetha Apts, Tadiwala Road, facet will be clean and sharp. In Pune-411001 stimulants or diamond look alikes the facet junctions are less sharp or [email protected] they appear rounded or moulded.

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