Volume 20 No. 2 April 1986 GAGTL EDU Set 3 ^eJournal of Gemmology GEMMOLOGICAL ASSOCIATION OF GREAT BRITAIN OFFICERS AND COUNCIL President: Sir Frank Claringbull Ph.D., F.InsLP., F.G.S. Vice-Presidents: J. R. H. Chisholm, M.A., F.G .A. R. K. Mitchell, F.G.A. H. J. Wheeler, F.G.A. Chairman: D. J. Callaghan, F. G. A. Vice-Chairman: N. W. Deeks, F.G.A. Honorary Treasurer: N. B. Israel, F.G.A. Fellows elected to Council: C. R. Cavey B. Jackson M. J. O'Donoghue, L. F. Cole C. B. Jones M. A., F.G.S. R. W. Croydon D. M. Larcher P. G. Read, C.Eng., P. J. E. Daly, B.Sc. D. Morgan M.I.E.E., M.LE.R.E. A. J. French G. Neary A. W. R. Round S. E. Hiscox J. B. Nelson, Ph.D., F.R.M.S., E. Stern J. A. W. Hodgkinson F. InsLP., F.G.S. C. H. Winter D. Inkersole W. Nowak, C.Eng., F.R.Ac.S. Branch Chairmen: Midlands Branch: C. L. Hundy, F.G.A. North-West Branch: S. Hill, F.G.A. Sowh Yorkshire & Distria Branch: J. I. Reynolds, F.G.A. Examiners: E. A. Jobbins,B.Sc., F.I.M.M., F.G.A. A. J. Allnutt, M.Se.,Ph.D., F.G.A. R. R. Harding, B.Sc., D.Phil., F.G.A. G. H. Jones, B.Se., Ph.D., F.G.A. D. G. Kent, F.G.A. E. M. Bruton, F.G.A. P. Sadler, B.Sc., F.G.S., F.G.A. C. Woodward, B.Se., F.G.A. A.E. Farn, F.G.A. M. Font-Altaba, D.Se. J. M. Bosch-Figueroa, D.Se. M. Virkkunen, M.Phil., F.G.A. Instructors: V. G. Hinton, F.G.A. S. B. NikonCooper, B.D., F.G.A. P. A. Waters, F.G.A. J. Edwards, F.G.A. D. Pratt, F.G.A. R. J. Peace, B.Se., F.G.A. Editor: E. A. Jobbins, B.Se., F.I.M.M., F.G.A. Consultant Editor: J. -R. H. Chisholm, M.A., F.G.A. Editorial Assistant: Mary A. Burland Curator: C. R. Cavey, F.G.A. Secretary: Con Lenan, F.G.A. Deputy Secretary: Jonathan Brown, Barrister-at-Law, F.G.A. Saint Dunstan's House, Carey Lane, London EC2V SAB (By Goldsmith's Hall) TeJephone:Ol~726 4374 J.Gemm., 1986,20,2 73 TheJournalof Gemmology VOLUME 20 NUMBER TWO APRIL 1986 Cover Picture Amerindian named 'Joseph' collecting jasper in the Ireng River at one of the Orinduik falls in Guyana, South America - see page 91. Photograph byJ.G. Gosling,F.G.A. ISSN: 0022-1252 7744 J.Gemm.,1986,20,J. Gemm., 1986,20,22 GEMMOLOGICAL INSTRUMENTS LIMITED GEMMOLOGICAA wholly owned subsidiaryL of theINSTRUMENT Gemmological Association ofS Great LIMITE Britain D A Saintwholly Dunstan'sowned subsidiar House,y of the CareyGemmologica Lane,l Associatio Londonn oEC2Vf Great 8ABBritai n SainTelephone:t Dunstan' 01-7264374s House, CareCables:y Lane Geminst,, Londo nLondon EC2V 8AEC2B Telephone: 01-726 4374 Cables: Geminst, London EC2 THTHEE RETAIRETAILL JEWELLER'JEWELLER'SS GEM TESTING SET y assembled t Dialdex Refractometer,GEM fluid and TESTIN case GStone SE tongs T Polarizing increasin yfilter gassemble pressur yed assemblett d t increasin4-prongy gassemble pressurstone holder y LEDassemble increasin idealighty assemble l sourcedfog t increasinrpressur ytrad assemblede ttestineg tpressurd t e t increasin ideaRaynery assemblel fog increasinrDiamondpressur ytrad assemblede ttestin eTesterg tpressurd increasing pressure t pressure t increasinOPL Spectroscopeidea increasingn l pressurfothre tradpremises ideag epressure tltestin for trade t e testin increasin ideaMoe increasingn l Diamond pressurfothre tradpremises ideag epressur e Gauge tltestin for trade ideal XIOfor tradZeisse lenstestin n the premises tradChelseae testin Colour nFilter the premises 'Gem idea Testingl fon ridea 'thtrad byel B.Wpremisesefo testinr trad. Andersone testin ideaRaynerl fon ridea thtrad Polariscopeel premisesefo testinr trad e testin n the premisesn the premisesn the premises e premisesn the premisesn the premises . 01'-"'0"") •e ..,I\\l!V-'1 TheThe RetailerRetailer SetSet hashas beenbeen especiallyespecially assembledassembled ttoo meemeett thethe needsneeds ofof thethe highighh streetstreet jewellejewellerr whowho isis undeunderr increasingincreasing pressurepressure ttoo identifyidentify gemstonesgemstones rapidly.rapidly. CompetitivelyCompetitively priced,priced, thethe SetSet isis idealideal forfor tradetrade testingtesting oorr satisfyingsatisfying customercustomer enquiriesenquiries onon thethe premises.premises. ToTo complementcomplement thethe Set,Set, a rangrangee ofof gemmologicalgemmological microscopemicroscopess andand gemstonegemstone specimensspecimens areare availableavailable fromfrom GemmologicalGemmological InstrumentsInstruments Limited.Limited. TheThe RetailerRetailer SetSet (Cat.(Cat. NoNo.. RjSl)RJS1) PricePrice £519.95£519.95 + pP & P + VATVAT JJ.. Gemm.,Gemm., 1986,20,21986, 20, 2 7755 NewNew developmentsdevelopments iinn spectroscopicspectroscopic methodmethodss forfor detectingdetecting artificiallyartificially colouredcoloured diamondsdiamonds G.S. Woods* and A.T. CollinsCollinst† * CSOCSO ValuationsValuations Ltd,Ltd, 1717 CharterhouseCharterhouse Street,Street, London,London, ECINEC1N 6RA6RA t† WheatstoneWheatstone PhysicsPhysics Laboratory,Laboratory, King'sKing's College,College, London,London, WC2RWC2R 2LS2LS IntroductionIntroduction FouFourr parameterparameterss ('the('the fourfour Cs'Cs')) normallynormally deter­deter­ minminee thethe valuevalue ofof a polishepolishedd diamondiamondd gemstone:gemstone: thethe caratcarat weight,weight, ththee cutcut,, ththee clarityclarity anandd thethe colourcolour.. ForFor Colourless a diamonddiamond ofof a givengiven weight,weight, withwith a well-propor­well-propor­ tionedtioned cucutt anandd a highighh claritclarityy grade,grade, ththee coloucolourr hashas a profounprofoundd influenceinfluence onon ththee valuvaluee ofof ththee stone.stone. DiamondDiamondss whicwhichh appearappear completelycompletely colourlesscolourless araree ververyy rarraree andand commancommandd ththee higheshighestt prices.prices. HoweverHowever,, a larglargee proportioproportionn ooff gegemm qualityquality diamonds,diamonds, belonginbelongingg ttoo ththee so-calledso-called CapeCape Series,Series, exhibitexhibit variouvariouss degreesdegrees ofof yellownessyellowness dowdownn ttoo a palepale w strawstraw colourcolour.. EvenEven a hinhintt ofof thisthis yelloyelloww colorationcoloration :::> Colourless - soso faintfaint thatthat a laymanlayman wouldwould notnot noticenotice itit -- «....J significantlysignificantly reducesreduces thethe valuevalue ooff ththee diamond.diamond. AsAs > thethe yelloyelloww coloucolourr becomebecomess moremore andand mormoree propro­­ nouncednounced,, soso thathatt iitt becomebecomess obviousobvious eveneven toto thethe untraineuntrainedd eye,eye, thethe valuvaluee ofof ththee diamondiamondd fallsfalls furtherfurther.. Occasionally,Occasionally, howeverhowever,, diamonddiamondss areare foundfound inin naturnaturee whichwhich areare ooff excellentexcellent gemgem qualityquality andand whichwhich havehave a full-bodiedfull-bodied yellow,yellow, goldegoldenn oorr amberamber colourcolour.. SuchSuch stonesstones araree termetermedd 'fancies''fancies'.. TheseThese DEPTH OF COLORATION diamondsdiamonds,, whewhenn properlproperlyy cutcut andand polishedpolished,, areare onon groundsgrounds ofof botbothh rarityrarity anandd attractivenesattractivenesss generallygenerally moremore valuablvaluablee thathann thosthosee withwith ththee lessless definitedefinite palepale FigFig.. 11.. ThiThiss diagramdiagram illustratesillustrates,, inin a schematischematicc way,way, howhow ththee yellowyellow colourcolourss ofof ththee loweslowestt categoriescategories ooff thethe CapeCape valuevalue ofof a cutcut andand polishedpolished diamonddiamond variesvaries withwith the the depth depth SeriesSeries.. InIn FigFig.. 1 wewe represenrepresentt iinn a schematicschematic wayway ofof yellowyellow colorationcoloration.. hohoww marketmarket forcesforces determindeterminee ththee valuevalue ofof diamondsdiamonds havinhavingg differendifferentt depthsdepths ofof yelloyelloww coloration.coloration. WeWe propertiepropertiess ofof diamonddiamond,, includingincluding investigationsinvestigations ofof noticnoticee thatthat,, althougalthoughh thethe strongly-colouredstrongly-coloured yellowyellow ththee poinpointt defectdefectss whicwhichh araree ththee originsorigins ofof colour,colour, fancyfancy diamonddiamondss areare nowhernowheree nearnear asas valuablevaluable asas andand thisthis iiss stillstill aann activactivee field ofof investigatioinvestigationn inin otherwiseotherwise comparablcomparablee colourlesscolourless stones,stones, thetheyy cancan manmanyy laboratories.laboratories. commandcommand a pricpricee welwelll aboveabove somesome ofof ththee diamondsdiamonds ThThee colourcolour produceproducedd bbyy irradiatioirradiationn andand heatingheating nearnear thethe middlmiddlee ooff ththee distribution.distribution. (called(called 'treatment''treatment' inin thethe gegemm tradetrade)) addsadds ttoo thatthat ResearchResearch worworkk onon diamondiamondd durinduringg ththee 1950s,1950s, alreadyalready presenpresentt inin thethe diamond.diamond. HenceHence,, consideringconsidering notablnotablyy bbyy Dugdale(I)Dugdale(1) andand ClarkClark anandd co-workers(2,3),co-workers(23), diamondsdiamonds frofromm neanearr ththee minimuminimumm poinpointt inin FigFig.. 1,1, showedshowed thathatt iitt was possiblepossible artificiallyartificially ttoo colourcolour thethe effecteffect ofof treatmenttreatment iiss toto intensifintensifyy theirtheir colour,colour, diamonddiamondss yelloyelloww oorr goldegoldenn bbyy subjectingsubjecting themthem toto anandd thusthus potentiallpotentiallyy ttoo enhanceenhance theirtheir value.value. AlthoughAlthough radiatioradiationn damagedamage inin a nuclearnuclear reactorreactor,, oror iinn a vavann dede manmanyy customercustomerss wouldwould bebe unablunablee