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Morgan - Abstract","","A brief review of gem faceting methods aims to enhance a stone’s visual appearance, supported by illustrations of cutting designs. It describes recently developed machines for producing concave facets and gives a detailed author-developed amateur machine, including encountered problems. An experiment compares refracted-ray patterns from a specially cut triangular prism, alongside computer-calculated theoretical ray paths, and features concave faceted CZ and fluorite stones with Nelson Gem Fingerprinter 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is the purpose of the reviewed faceting methods in this document?","Question",{"text":112,"@type":113},"The document reviews gem faceting methods intended to enhance the stone’s visual appearance and scintillation, using illustrations of various special cutting designs.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"What does the document describe about concave-facet machines?",{"text":117,"@type":113},"It illustrates and discusses machines recently developed to produce concave facets, and it provides a detailed description of an author-made amateur machine and the problems encountered with that approach.",{"name":119,"@type":110,"acceptedAnswer":120},"How are special effects achieved in the cutting process?",{"text":121,"@type":113},"Special effects are produced by deliberately cutting selected pavilion facets at angles below the critical ideal and by applying techniques such as frosting certain facets to create contrasting 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Britain  \nGemmological Associationand Gem Testing Laboratoryof Great Britain  \n27 Greville Street,London EC1N 8TNTel:02074043334Fax:02074048843e-mail:gagtl@btinternet.com Website:www.gem-a.info  \nPresident:  \nProfessor A.T.Collins  \nVice-Presidents:  \nN.W.Deeks,A.E.Farn,R.A.Howie,D.G.Kent,R.K.Mitchell  \nHonorary Fellows:  \nChen Zhonghui,R.A.Howie,K.Nassau  \nHonorary Life Members:  \nH.Bank,DJ.Callaghan,E.A.Jobbins,H.Tillander  \nCouncil of Management:  \nTJ.Davidson,R.R.Harding,I.Mercer,J.Monnickendam,  \nM.J.O'Donoghue,E.Stern,I.Thomson,V.P.Watson  \nMembers'Council:  \nA.J.Allnutt,S.Burgoyne,P.Dwyer-Hickey,S.A.Everitt,J.Greatwood,  \nB.Jackson,L.Music,J.B.Nelson,P.G.Read,P.J.Wates,C.H.Winter  \nBranch Chairmen:  \nMidlands-G.M.Green,North West-D.M.Brady,Scottish-B.Jackson,  \nSouth West-R.M.Slater  \nExaminers:  \nA.J.Allnutt,M.Sc.,Ph.D.,FGA,L.Bartlett,B.Sc.,M.Phil.,FGA,DGA,S.Coelho,B.Sc.,FGA,DGA,Prof.A.T.Collins,B.Sc.,Ph.D,A.G.Good,FGA,DGA,  \nJ.Greatwood,FGA,G.M.Howe,FGA,DGA,S.Hue Williams MA,FGA,DGA,  \nB.Jackson,FGA,DGA,G.H.Jones,B.Sc.,Ph.D.,FGA,Li Li Ping,FGA,DGA,  \nM.Newton,B.Sc.,D.Phil.,C.J.E.Oldershaw,B.Sc.(Hons),FGA,DGA,  \nH.L.Plumb,B.Sc.,FGA,DGA,R.D.Ross,B.Sc.,FGA,DGA,P.A.Sadler,B.Sc.,FGA,DGA,  \nE.Stern,FGA,DGA,S.M.Stocklmayer,B.Sc.(Hons),FGA,Prof.I.Sunagawa,D.Sc.,  \nM.Tilley,GG,FGA,C.M.Woodward,B.SCc.,FGA,DGA  \nThe Journal of Gemmology  \nEditor:Dr R.R.Harding  \nAssistant Editors:M.J.O'Donoghue,P.G.Read  \nAssociate Editors:Dr C.E.S.Arps(Leiden),  \nG.Bosshart(Zurich),Prof.A.T.Collins (London),Dr J.W.Harris(Glasgow),Prof.R.A.Howie(Derbyshire),Dr J.M.Ogden(Hildesheim),  \nProf.A.H.Rankin(Kingston upon Thames),Dr J.E.Shigley(Carlsbad),  \nProf.D.C.Smith(Paris),E.Stern (London),Prof.I.Sunagawa(Tokyo),  \nDr M.Superchi(Milan),C.M.Woodward (London)  \nProduction Editor:M.A.Burland  \n# Development ofconcave faceting of gemstones\n\nA.D.Morgan  \nBirmingham,West Midlands  \nABSTRACT:A brief review of gem faceting methods intended toenhance the visual appearance of the stone is introduced,withillustrations of stones with various special cutting designs.Machinesrecently developed for producing concave facets on gem stones areillustrated and discussed.A detailed description of a machine foramateur use developed by the author is given,and the problemsencountered in this method of faceting are outlined.The result of anexperiment with a specially cut triangular prism having simple flat andcylindrically concave facets to compare the refracted ray patterns isshown,together with the computer-calculated theoretical ray path of apencil of light impinging on a combination of concave lenslets andconvex mirrors.Two concave faceted stones cut by the author,one in CZand one in fluorite are featured and the patterns obtained with a NelsonGem Fingerprinter are illustrated.  \nKeywords:Concave facet,faceting,gem cutting machines  \nplacing and polishing of flat facets.This hasresulted in the development of standard cutsfor round brilliants and other shapes togive maximum brilliance and weight yieldfrom the rough crystal.  Furtherdevelopments include the introductionof the Profile(Princess)cut by Arpad Nagy(1960),which has a series of V-grooves cutinto the back of the stone,enablingflat crystals to be cut economically,and theBarion Cut by Basil and Marion Watermeyer(c.1970).  \n“is it original  \nit was once I answered truthfullyand may be again”  \ndon marquis,1930  \n## Introduction\n\nThe faceting of rough gem material toproduce an optically attractive gem isa highly specialized and skilled art.Over many years,several facet designsclaiming to enhance visual appearance andscintillation have been published.This isparticularly so in the case of diamond,where apart from its colour and weight aconsiderable proportion of the value of thestone is related to the geometry and correct  \nIn the case of coloured ","cbCaiep88mbY9Gyi","https://ap.wps.com/l/cbCaiep88mbY9Gyi","pdf",9197377,68,"English","# Development of concave faceting of gemstones\n## Abstract\n## Introduction\n## Cutting for special effects","[{\"question\":\"What is the purpose of the reviewed faceting methods in this document?\",\"answer\":\"The document reviews gem faceting methods intended to enhance the stone’s visual appearance and scintillation, using illustrations of various special cutting designs.\"},{\"question\":\"What does the document describe about concave-facet machines?\",\"answer\":\"It illustrates and discusses machines recently developed to produce concave facets, and it provides a detailed description of an author-made amateur machine and the problems encountered with that approach.\"},{\"question\":\"How are special effects achieved in the cutting process?\",\"answer\":\"Special effects are produced by deliberately cutting selected pavilion facets at angles below the critical ideal and by applying techniques such as frosting certain facets to create contrasting patterns.\"}]","Development ofconcave faceting of gemstones - A.D. Morgan - Abstract | PDF",1792993849,171]