GemmoloGy

It is said that Alexander the Great found a valley full of both diamonds and poisonous snakes.

No one could work out how to retrieve the jewels until Alexander had the idea of throwing down raw meat, to which the diamonds attached. When eagles flew down for the meat, Alexander's men just had to follow them to their nests. It sounds like fantasy but diamonds are attracted to fat, and the story reminded people how to tell real diamonds from fakes. De Beers still practice Alexander's trick in their South Africa mines today: They use "grease tables" and only the valuable stones stick.

This test is very much valid even in day-to-day diamonds business. Those who do diamond assorting can vouch for it. every sorter lifts the diamond just by touching the stone with a finger and the diamond gets lifted due to the slight oily nature of the human finger, whereas all other white coloured stones simply fall off the finger. many who do this daily don’t know why this happens. It’s the property of diamond to get attracted to grease or oily surface. The human sweat has some oil content in it which is responsible for the diamonds sticking to the finger.

This is also very important for those who are starting business in

diamonds. one should always open star sized diamond packet carefully and slowly. If you want to pick up a

stone then do so only with a stone holder or tweezer. Never move your fingers through the diamonds, you would never know how many diamonds would get stuck to your fingers and fall out.

Visual Methods

Tilt TestThe high Refractive Index (RI) of Diamond makes possible a simple test to distinguish it quickly from simulants with lower RIs. Hold a brilliant-cut diamond in a pair of tweezers with its table face up, horizontal below the eye. Tilt the stone away from the body and observe the table facet. If the stone is a diamond, the amount of brilliancy coming from the table will be the same. However if this test is carried out on brilliant-cut stones of lower RI, such as yAG or paste, the light will appear to empty out from the stone. This test can also be carried out on mounted stones Read through Test

Diamond has a low Critical Angle of 24ْ 26’, which means that a brilliant-cut stone reflects back most of the light entering it. It is therefore impossible to look right through a perfect brilliant cut diamond from the table and see what is below. except through the culet, if it is large enough, anything would be visible.

Draw a line on a piece of paper and place the stone with its pavilion face up. In case of a diamond the line will not be seen at all. In the

case of simulants, the line will appear partially or complete. This test can be easily carried out on unset stones; but care must be taken when they are mounted.

Confusion is possible with old cut diamonds, in which full advantage of the low critical angle was not taken in cutting. Here, the line may appear unnaturally clear or transparent for diamonds. The large culet and the facet edges will be immediately apparent to the naked eye through the table. This results from the larger angle of the pavilion facets, which allow light to escape through the back of the stone.

Not all diamonds would give the read through test. Therefore be careful of all fancy cut diamonds, Fish-eye stones or diamonds with shallow pavilion depth.As well as stones like Strontium Titanate (same RI of 2.41) and Synthetic moissanite (a DR stone with RIs of 2.648-2.691 and Double Refraction (0.043) which may not give that effect. Breath Test

As diamonds have high thermal conductivity there is simple test for identifying diamonds from its simulants. Because of its high thermal conductivity, diamond feels colder to touch, any other gemstones. It is cold to touch and becomes warm quickly, when worn. If a loose stone or diamond jewellery is left to attain room temperature and then touched, it will feel quiet cold. In this test the stone to be tested is taken along

Identifying DiamondsDiamond 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.

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JAYSHREE PANJIKARPangem testing laboratory10 sangeetha apts, tadiwala road,Pune-411001jayshreepanjikar@gmail.com

with a known diamond. When you breathe on the clean surface of a diamond, the mist that is formed, will clear much faster in case of the diamond than when compared to its simulants. care should be taken to ensure that both the stones are at room temperature when the test is taking place. the recent synthetic moissanite also has a good thermal conductivity would therefore give similar reaction. Water Test

Diamond has a very high surface tension, therefore if the table surface of a diamond is thoroughly clean and free of grease, a drop of water on the table will remain as a globule for a long time, whereas in case of other stones / simulants, the globule will spread out in a relatively short time, depending on the mineral. Tests using a 10x lens

Polishing lines: Diamonds has directional hardness and therefore the polishing lines run in different directions on different facets. this means that there are no two adjacent facets having polishing lines in the same direction. in case of simulants, the polishing lines always run in the same direction on all facets. this is a confirmatory test for identifying diamonds. Bearding: in the manufacturing process of diamond there is the bruting process in which two diamonds are rubbed against one another in order to form the girdle. if there is a vibration between the two diamonds (due to careless handling) then in the polishing diamond it will produce hair like feathers / cracks / whiskers running from the girdle into the stone. this is known as bearding and it occurs due to the cleavage property of diamonds. Facet Junctions: Diamonds exhibit sharp, knife-edge like facet junctions, due to their highest hardness. When seen under a 10X lens, the edges of the diamond facet will be clean and sharp. in stimulants or diamond look alikes the facet junctions are less sharp or they appear rounded or moulded.

even after many years of constant wear, cut diamonds preserve their sharp edges and corners, while most other gemstones become worn and chipped. most simulants after a few years of wear have rounded or moulded edges between facets.

Gridle Appearance: the girdle of a brilliant-cut diamond is different in appearance from that of other stones. it appears sugary or granular, if it is unpolished. in case of simulants the girdle would appear smooth and glass-like. the girdle of a diamond has a matt, waxy appearance, caused by the fracturing process of bruting. it is not dull like ground glass, but has a shiny wax-like lustre. this is confirmatory test for identifying only round brilliant cut (rBc) diamonds.

Presence of naturals: a natural on the girdle is an indication of diamond. it is the part of the original skin of the rough diamond left on the stone and usually looks much brighter than the girdle. a natural indicates that the cutter has tried to retain the maximum weight from the rough crystal. a natural may show surface markings in the form of trigons, cube markings or parallel lines. trigons may be seen on the natural, when they are part of an original octahedral face. this is a confirmatory test.

Naturals are good proof that the stone is a diamond, but there is one simulant – Yttrium aluminate or Yttrium aluminium Garnet (YaG, also called Diamonair) – where similar naturals are occasionally left, during manufacturing (by czochralski method). But its ri of 1.833 is much lower than that of diamond.

Doubling of Backseats: synthetic moissanite is the only diamond simulant with thermal

conductivity high enough to fool many of the thermal testers on the market, but it is easily distinguished from diamond with 10x magnification. Because synthetic moissanite is Doubly refractive (unlike diamond, which is singly refractive), inclusions and back facet junctions will appear doubled. however, since synthetic moissanite is often faceted with the table perpendicular to the optic axis, you should examine a suspect stone from multiple angles to check for doubling. Viewing through several bezel facets will usually produce the best results.

some inclusions that might be seen in synthetic moissanite are open, not-quite-parallel, tube-like channels. they are usually hexagonal in cross section, and might be capped by other inclusions. these will appear doubled under magnification, unlike the etch channels sometimes seen in natural diamond. Other possible inclusions are slender white needles, very fine refractive lines and pinpoints that are sometimes numerous enough to form clouds.■ —By Jaushree Panjikar