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University of British Columbia
Earth and Ocean Sciences
EOSC 118

Module A Lesson 11Study Notes The 4 Cs Cut and polished diamonds are evaluated by four primary variables all beginning with the letter C hence the 4 CsWhat are the 4 Cs for evaluating polished diamonds ColourClarityCutCaratAll variable are equally important and it is their unique combination that defines the value of a diamond Who introduced the 4 C system De Beers in the late 1930s Since then the 4 C system has become standardized and has gained widespread use by gemological libraries like GIA EGL and jewelers and consumers Variations on the 4 Cs have been used for other gemstones as well but not to the same extent as with diamondsIdentify and explain the fifth C A fifth C has been proposed in recent years to reflect the stones country of origin The fifth C has bearings on the historical significance of the stone but more importantly it determines whether or not the stone came from conflict zones The image and video link below are about a wonderful faceted gemstone which it is not a diamond The mineral is called cerussite and is a lead carbonate with particularly high average refractive index and dispersion Terri Ottaway of the Royal Ontario Museum speaks about the properties of this particular gemstone and the difficulty of the cutting processa nice primer before understanding the 4 CsThe Light of the Desert a faceted cerussite PbCO from 3Namibia 898 carats Image from the Royal Ontario MuseumCut The External Anatomy of a Gemstone What does the cut of a gemstone refer to The quality of the facets that define the stones proportions Cut is not to be confused with the shape of a cut gemstone round brilliant cushion pear etcThis C is probably the least understood intuitive and appreciated of the four What role does cut play in the quality of the gemstone Cut plays a huge role in the gems resulting optical effects of fire and brilliance Cut can also have a significant impact on the weight of the stone carat For example stones with the same faceup diameter can differ in weight depending on how thick the cutlet or pavilion is What is the difference between a poor and excellent cut Poor cuts are too shallow ortoo deep which can leave the stone dull and lacking life An excellent cut will return all the light entering the stone back to the eye through the top or table of the stone Stones with excellent also known as ideal cut will show good symmetry of facets as well as good length to width ratios when comparing the topdown dimensions of the table and full diameterIn moderncut gemstones the culet is often absent from the final shape or at least very smallSimplified anatomy of a Round Brilliant cut diamond
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