Diamond Grading
Diamond clarity is the quality of diamonds that relates to the existence and visual appearance of internal characteristics of a diamond called inclusions, and surface defects, called blemishes. Clarity is one of the four Cs of diamond grading, the others being carat, color, and cut.
Inclusions are solids, liquids, or gases that were trapped in a mineral as it formed. They may be crystals of a foreign material or even another diamond crystal or may have produced structural imperfections, such as tiny cracks that make a diamond appear whitish or cloudy. The number, size, color, relative location, orientation, and visibility of inclusions can all affect the relative clarity of a diamond. A clarity grade is assigned based on the overall appearance of the stone under ten times magnification, which is a magnification standard for loupes used in the gem world.
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DIAMOND GRADING
CHEMICAL COMPOSITION: Different form of carbon (graphite, amorphous, diamond.)
GEOLOGICAL OCCURENCES AND THEIR HISTORY : Gem and Industrial diamond, kimberlite (mines); Alluvial deposits (river beds); Marine deposits (beaches, sea-bed); Meteoric diamonds; localities like Australia’ Borneo’ Brazil’ India’ Sierra Leon, Russia; South Africa; South West Africa; Zaire, Canada etc.
EXTRACTION OF DIAMONDS : Crushing, Washing ad Screening, Heavy media separator; Grease table, Grease belt, X-ray separation.
OPERATION OF THE MARKET : De-Beers consolidated Mines; Diamond Trading Company (D.T.C.); Sights supplied by D.T.C. Diamond Brouses; Clubs; Operation of the national and International markets. Sources of Rough diamonds : HDC, MMTC, NDMC, Local-resellers, DTC, Open Market.
OPTICAL PROPERTIES : Single and anamolous double refraction, Refractive index; Absorption spectra.
HISTORY OF CUTS : The modern brilliant cut; Variation of te brilliant cut; Principles of diamond cutting; Lustre, brilliance, fire, ideal cuts and proportions; variation from the ideal cut.
MANUFACTURING OF DIAMONDS : Grains; Sawing; Cleaving; Bruiting; Grinding; Polishing; 4,3,2 point stones; Acidising; Ultrasonic cleaning.
COLOUR GRADING OF POLISHED STONES : Lighting standards and magnification; Comparison stones. Colour grading systems (G.I.A.; Indian)
CLARITY GRADING OF POLISHED STONES : Magnification; Lighting; International grading scales; (G.I.A.); Criteria for grading; Internal blemishes; External defects.
GRADING FOR CUT : Spread stones; Lumpy and Fish-eye stones, Proportion scope and proportion analyzing, Carat system; Weighing scales; Sieves and sieve sizes.
SYNTHETIC DIAMOND : Synthesis; Artificial clouration; Identification of treated diamond.
IDENTIFICATION OF DIAMOND : With 10x only; With Instruments; Type; Classification.
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