Gemstones Exam Review - Lecture #1 Separating Diamond from...

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Unformatted text preview: Lecture #1 Separating Diamond from its Simulants Cut around the edges and try and keep a piece of the original diamond on the edge to show they cut limited amounts to obtain final product There are only 2 minerals in which an inclusion can occur in: garnet and diamond very Can tell the difference between a diamond and cubic zirconium by the lustre of the gem being observed. Zirconiums higher dispersion is greater than that of diamonds and gives more fire Look over table 17.3 and memorize key features (diamond, cubic zirconium) Tests to identify diamond stimulants since RI of diamond is too high for a refractometer Visual Observations: 1) Light Spill or Tilt Test (RI and cutting proportions) You are projecting black background from under the gemstone. If it gets through then it isnt a diamond because light from the top is reflected back. With a high reflective index, the black background will not get through 2) Dot-Ring Test (RI and cutting proportions) Best for unmounted stones draw a small black dot on paper, put table facet down centered on dot. If stone has a smaller refractive index than diamond the dot will be visible as a ring around the culet of the stone (note: shallowly-cut diamonds will fail this test). The effect is due to the failure of the pavilion facets to act as internal mirrors, allowing dots to show through the pavilion facets as a ring. 3) Transmission Test (RI and cutting proportions) same as dot ring test but placed down on a strongly-colored surface. If the color does not show through, it must be either a diamond, strontium titanate, rutile, synthetic moissanite, or a simulant with a deep cut pavilion (note shallowly-cut diamonds will fail this test) 4) Facet Condition Test (Hardness) Another visual test Test to identify diamond stimulant using the Reflectometer Instrument: 1) Reflectance Test (RI) Because of diamonds high RI (and that of several of its simulants) it is not possible to measure it on a refractometer. However, since there is a direct relationship between RI and reflectivity, an electronic reflectance meter can determine if its refractive index is high enough to possibly be diamond Other tests to identify diamond stimulants: 1) Thermal Conductance Test (Thermal Conductance Meter) With the exception of synthetic moissanite (which can be detected by its large double refraction), diamond has a very much greater thermal conductance than ANY of its simulants. Thus one of the most widely used checks for diamond is made with the aid of a thermal conductance tester. A metal probe is placed on the diamond and one of its surfaces is placed on a metal plate. The heat moving through the diamond is large, and if it passes a certain threshold, it must be a diamond or synthetic moissanite 2) Weight/Girdle Diameter Test (SG) Best with well proportioned roundbrilliant cut diamonds. Using an unmounted stone, weigh it and measure its diameter. The ratio of weight to diameter can be used to separate diamond from CZ, YAG, GGG and Strontium Titanate Lecture #2...
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This note was uploaded on 10/11/2010 for the course ECONOMICS ECON 1B03 taught by Professor Holmes during the Fall '08 term at McMaster University.

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Gemstones Exam Review - Lecture #1 Separating Diamond from...

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