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Home , Base metal, Carat (mass), Copper, Depletion gilding, Fineness, Gold

PRECIOUSPRECIOUS METALSMETALS

MetallurgyMetallurgy andand RelatedRelated TopicsTopics By AldoAldo M.M. RetiReti Topics:Topics:

„ MetallurgicalMetallurgical AspectsAspects „ GoldGold „ Karat System „ Legal Aspects, Hallmarking „ , practical example of Color Matching „ Depletion , Leaf „ Gold Filled „ SilverSilver (Ag/Cu(Ag/Cu System),System), „ CaseCase StudyStudy: Embrittlement of Ancient „ PlatinumPlatinum (Pt(Pt Alloys)Alloys) WhyWhy “Precious”?“Precious”?

„ Expensive,Expensive, Rare,Rare, DesirableDesirable „ NobleNoble „ Tradition,Tradition, HistoryHistory „ Gold „ Silver „ „ PGM (Platinum, , , , , ) „ UsuallyUsually Alloyed,Alloyed, inin orderorder toto enhanceenhance properties:properties: „ Mechanical „ Color „ “Extend Use” GoldGold AlloysAlloys

WhatWhat isis Important?Important?

•• HowHow muchmuch Gold?:Gold?: KaratKarat SystemSystem KaratKarat SystemSystem ()(Carat)

„ Karat:Karat: GoldGold Content,Content, expressedexpressed inin 24ths24ths Karat (ppt)

24 1000 22 916.7 18 750 14 583.3 10 416.7 9 375 8 333.3 GoldGold AlloysAlloys

WhatWhat isis Important?Important?

•• HowHow muchmuch Gold?:Gold?: KaratKarat SystemSystem „ ColorColor ColorsColors ofof GoldGold

„ DeterminedDetermined byby AlloyingAlloying ElementsElements „ “Classic”“Classic” System:System: Au/Cu/AgAu/Cu/Ag (and(and Zn)Zn) isis thethe basisbasis forfor “Colored“Colored ”Golds” „ YellowYellow „ RedRed „ GreenGreen „ “White“White Golds”:Golds”: Au/Cu/NiAu/Cu/Ni oror Au/Ag/PdAu/Ag/Pd (Ni(Ni andand PdPd areare veryvery strongstrong goldgold “whiteners”)“whiteners”) NickelNickel AllergyAllergy

Unfortunately, many people, the female population especially, are allergic to in contact with the skin and this gives rise to a red skin rash or irritation. The countries have enacted legislation valid from the 20th January 2000 that limits nickel release from . Thus, in , nickel white golds are being phased out and being replaced by palladium white golds. The USA is taking a more relaxed approach, requiring jewellery to be labelled as nickel- containing, and much jewellery in the West is now advertised as 'non-allergenic' or 'nickel-free'. (See article in Gold , No 28, Spring 2000, "Nickel gets under your skin“) GoldGold AlloysAlloys

WhatWhat isis Important?Important? „ HowHow muchmuch Gold?:Gold?: KaratKarat SystemSystem „ ColorColor „ PropertiesProperties –– UtilizeUtilize PhasePhase Diagrams!Diagrams! „ Strength,Strength, HardnessHardness „ WorkingWorking CharacteristicsCharacteristics „ CastabilityCastability (melting(,point, fluidity)fluidity) „ (lost process, ) TernaryTernary CompositionComposition DiagramDiagram GoldGold ColorColor DiagramDiagram ColorColor cancan bebe Measured!Measured!

CIELABCIELAB ColorColor SystemSystem

„ InternationalInternational SystemSystem „ AdoptedAdopted inin 19761976 byby thethe InternationalInternational CommitteeCommittee onon IlluminationIllumination „ ASTMASTM StandardStandard „ ClassicClassic ExampleExample ofof Use:Use: PaintPaint IndustryIndustry CIELABCIELAB SystemSystem

„ UsesUses 33 Coordinates:Coordinates:

„„“L”“L” forfor BrightnessBrightness (100=white, 0=black)

„„“a”“a” forfor RedRed--GreenGreen (100=red, -100=)

„„“b”“b” forfor YellowYellow--BlueBlue (100=yellow, -100=) „ Thus,Thus, ColorColor cancan bebe representedrepresented byby aa vectorvector inin 33 coordinatecoordinate spacespace

HowHow toto MeasureMeasure Color?Color?

„ SpectrophotometerSpectrophotometer „ Manufacturers:Manufacturers: „ MacbethMacbeth „ HunterHunter LaboratoriesLaboratories „ BYKBYK GardnerGardner „ AppliedApplied ColorColor SystemsSystems (ACS)(ACS) ExamplesExamples ofof ColorColor

LL aa bb

GoldGold 84.084.0 4.84.8 34.334.3 SilverSilver 95.895.8 --0.70.7 5.35.3 CopperCopper 84.084.0 11.811.8 14.314.3 70/3070/30 BrassBrass 91.191.1 --4.14.1 22.022.0 ColorColor VariationVariation inin 1414 KtKt AlloysAlloys

ColorColor LimitsLimits aa LimitsLimits bb

RedRed >> 3.53.5 15.015.0 toto 23.023.0 YellowYellow --1.01.0 toto 3.53.5 18.518.5 toto 23.023.0 GreenGreen --1.01.0 toto --5.55.5 17.017.0 toto 23.023.0 WhiteWhite --1.01.0 toto 1.01.0 lessless thanthan 12.012.0 ColorColor DifferenceDifference

ColorColor ofof metalmetal 1:1: LL1,, aa1,, bb1

ColorColor ofof metalmetal 2:2: LL2,, aa2,, bb2

2 2 2 2 DD == (L(L2--LL1)) ++ (a(a2--aa1)) ++ (b(b2--bb1))

Human eye can differentiate D>2 Composition of 51 14Kt Au/Cu/Ag/Zn Alloys (D.P. Agarwal and G. Raykhtsaum, “The Santa Fe Symposium onon Jewelry Technology”, 1988, pp. 229-244) ConstantConstant “L”“L” LinesLines forfor 1414 KtKt Au/Cu/Ag/ZnAu/Cu/Ag/Zn AlloysAlloys ConstantConstant “a”“a” LinesLines forfor 1414 KtKt Au/Cu/Ag/ZnAu/Cu/Ag/Zn AlloysAlloys ConstantConstant “b”“b” LinesLines forfor 1414 KtKt Au/Cu/Ag/ZnAu/Cu/Ag/Zn AlloysAlloys ExampleExample ofof “Color“Color Matching”Matching”

„ OldOld piecepiece ofof goldgold alloyalloy needsneeds toto bebe matchedmatched (repaired)(repaired) withwith aa newnew 14Kt14Kt alloyalloy „ MeasureMeasure colorcolor ofof oldold piecepiece „ Say,Say, LL == 9393 aa == --4.54.5 bb == 19.519.5 „ NowNow gogo toto ternaryternary chartscharts toto findfind compositioncomposition ofof 1414 KtKt alloyalloy withwith bestbest matchmatch ConstantConstant “L”“L” LinesLines forfor 1414 KtKt Au/Cu/Ag/ZnAu/Cu/Ag/Zn AlloysAlloys

L=93.0 ConstantConstant “a”“a” LinesLines forfor 1414 KtKt Au/Cu/Ag/ZnAu/Cu/Ag/Zn AlloysAlloys

a= -4.5 ConstantConstant “b”“b” LinesLines forfor 1414 KtKt Au/Cu/Ag/ZnAu/Cu/Ag/Zn AlloysAlloys

b=19.5 Composition of 51 14Kt Au/Cu/Ag/Zn Alloys (D.P. Agarwal and G. Raykhtsaum, “The Santa Fe Symposium onon Jewelry Manufacturing Technology”, 1988, pp. 229-244)

Desired L, a and b are within red circle: 70% Ag, 20% Cu, 10% Zn BestBest ColorColor MatchMatch 1414 KtKt AlloyAlloy

Silver:Silver: 70%70% xx 41.67%41.67% == 29.17%29.17% :Copper: 20%20% xx 41.67%41.67% == 8.33%8.33% :Zinc: 10%10% xx 41.67%41.67% == 4.17%4.17% Gold:Gold: == 58.33%58.33% 100.00%100.00% PurplePurple GoldGold

„ Purple gold (also known as or violet gold) When gold and are alloyed in a certain fixed ratio, they form a gold compound with the chemical formula AuAl2 (or Au6Al11). That is one of gold to two of aluminium. This compound has an attractive purple color. In terms of composition, this compound is about 79% gold by and hence is hallmarkable as 18 carat gold.

„ All intermetallic compounds, and purple gold is no exception, tend to be very brittle. They cannot be easily worked by conventional working processes. If one attempted to roll or a piece of purple gold, it would shatter into pieces!

„ “Purple Plague” when bonding gold to aluminum. BlueBlue GoldGold

„ AuAu--FeFe AlloysAlloys (i.e.,(i.e., 7575 AuAu--2525 Fe)Fe) „ AuAu--InIn AlloysAlloys „ ColorColor InterferenceInterference effecteffect causedcaused byby thinthin filmfilm ofof oxideoxide onon surfacesurface „ PurplePurple filmsfilms foundfound inin TutankhamunTutankhamun goldgold (presence(presence ofof FeFe andand As)As) DepletionDepletion GildingGilding

„ “Coloring“Coloring thethe Gold”.Gold”. SurfaceSurface richrich inin gold.gold. RemoveRemove basebase metalsmetals fromfrom thethe surface,surface, whichwhich isis enrichedenriched inin gold.gold. „ Process:Process: conversionconversion ofof basebase metalsmetals nearnear thethe alloyalloy surface:surface: „ Chemical attack ( and common ), applied to Guanin (silver-rich). Form silver and copper chlorides, which at high are absorbed by the (cementation) „ Oxidation/, applied to (copper-rich) „ ModernModern Method:Method: ChemicalChemical “Bombing”“Bombing” „ Hot + peroxide DepletionDepletion GildedGilded TumbagaTumbaga fromfrom thethe VicusVicus ,Period, PeruPeru CrossCross--SectionSection ofof aa VicusVicus DiscDisc (x200)(x200) DepletionDepletion GildingGilding

Tribes in Pre-Columbian , specifically the Moche and later the Chimu who were located in northern coastal Peru from between 250 BC to 600 AD and 800 AD to 1500 AD, respectively, hammered copper alloys to make ornamental objects. Pre-Columbian specialized in a copper called tumbaga, which is primarily gold and copper, perhaps with some silver because silver typically occurs with gold when found in Andean stream beds. Tumbaga can achieve a gold color, despite being as low as twelve percent gold through a process called . Depletion gilding requires a sheet of tumbaga in an acidic solution. Acidic pickling could be easily obtained by the Moche and Chimu by soaking certain plant roots. The pre-Columbian Peruvian's primary interest in stems from a strong sense of spirituality. They believed that a divine power gave them the ability to "magically" make and designs appear in materials from where they had not previously existed, such as bringing a gold color out of a copper colored alloy. One can clearly see how the pre-Columbians would see depletion gilding a copper colored alloy and making it turn gold as a very spiritual activity since they did not understand the metallurgical principles behind depletion gilding. 99 KtKt GoldGold--SilverSilver AlloyAlloy treatedtreated 77 hourshours atat 165165 CC inin alumalum pastepaste (x250)(x250) 99 KtKt GoldGold--SilverSilver--CopperCopper AlloyAlloy afterafter 99 cyclescycles ofof torchtorch heatingheating inin alumalum pastepaste (x400)(x400) GoldGold LeafLeaf

„ Few millionths of an inch thick (about 1/10 ) „ Dates back….5,000 years?.... 1352 B.C., King Tutankhamun „ Mechanical method, no heat. Two dimensional tensional stresses and compression in the third direction „ Gold with ~ 4% Silver. Also, some Copper (all have same ) „ Formation of new “sub-grains” as the gold alloy is worked „ Decorative uses, resistance to . , altars, printing, buildings Beating technique: Gold is first rolled into ribbons 1/1,000” thick, then cut into 1 1/4” squares and placed in squares of seaweed , encased in turn in parchment paper. This packet, called a “cutch”, is then squeezed in a press to compress the paper. The “cutch” is then beaten with a 17 lb hammer until the gold is in 4 inch squares. These are then placed in ox skins, coated with brime, a powder-like substance made from volcanic ash, brushed on with the hind leg of a Russian hare. This new packet, a “shoder” is beaten for 2 hours with a 9 lb hammer, then divided again into a “mould” wrapped in parchment paper, which is beaten with a 7 lb hammer. In all, about 82,800 blows are necessary to reduce the gold to 3 millionths of an inch in thickness. The gold is then so delicate that it can be cut only with a malacca reed shaped into a ccuuttingtting tool or “wagon” which is slid across the gold. (From: The Gold Companion, by Timothy Green). CorrosionCorrosion ofof GoldGold

„ DoesDoes GoldGold ?Tarnish? „ Tarnish:Tarnish: discoloration of metal surface caused by a thin layer of a reaction product ( or sulphide) „ KaratKarat dependent,dependent, i.e., 14 Kt contains ~~ 3030 toto 3535 volumevolume percent gold, the rest are „ Agents:Agents: , food, perfumes, household cleaners, etc. Also, are sometimes of lower karat RESOURCESRESOURCES

„ www.gold.org „ Gold Technology „ Gold Bulletin „ MJSA www.mjsainc.com „ AJM Magazine www.ajm-magazine.com „ Annual Show „ The Santa Fe Symposium on Jewelry Manufacturing Technology www.santafesympowww.santafesymposium.orgsium.org „ International Precious Metals Institute www.ipmi.org „ Hallmarking Office www.theassayoffice.co.uk „ Federal Trade Commission www.ftc.gov „ The Silver Institute www.silverinstitute.org „ Platinum Metals Review www.platinummetalsreview.com „ Platinum Guild International www.pgi-platinum-tech.com „ FEM (Institute for Precious Metals, ) www.fem-online.de „ Books: W.S. Rapson, “Gold Usage”, Academic Press (1978) A. Butts and C.D Coxe, “Silver, Economics, and Use”, Van Nostrand (1967) T. Green, “The Gold Companion”, Rosendale Press Ltd. (1991) ResourcesResources (Cont.)(Cont.)

„ MaterialsMaterials andand Supplies:Supplies: ConservationConservation ResourcesResources InternationalInternational LLCLLC http://www.conservationresources.com/Main/S%20CATALO G/CoverPage.htm

„ ForFor GoldGold Products:Products: http://www.utilisegold.com/http://www.utilisegold.com/ AnotherAnother ResourceResource

„ ©The©The AmericanAmerican InstituteInstitute forfor ConservationConservation ofof HistoricHistoric && ArtisticArtistic WorksWorks 17171717 KK StreetStreet NW,NW, SuiteSuite 200200 Washington,Washington, DCDC 2003620036--53465346 202202--452452--95459545 202202--452452--93289328 (fax)(fax) http://aic.stanford.edu/about/index.htmlhttp://aic.stanford.edu/about/index.html

The American Institute for Conservation of Historic and Artistic Works (AIC) is the national membership organization of conservation professionals dedicated to preserving the art and historic artifacts of our cultural heritage for future generations. GoldGold FilledFilled

„ IsIs itit filledfilled withwith gold?gold? „ EarlyEarly applications,applications, wrappingwrapping goldgold aroundaround aa metalmetal rod,rod, fusingfusing itit andand drawndrawn intointo wire,wire, thus:thus: “gold,“gold, filledfilled withwith basebase metal”metal” HowHow isis G.F.G.F. oror R.G.P.R.G.P. Made?Made? ComponentsComponents forfor GoldGold FilledFilled SheetSheet 1818 KtKt GoldGold onon BrassBrass 1/561/56 1010 KtKt GoldGold onon NickelNickel 1/201/20 1414 KtKt GoldGold onon PhosphorPhosphor BronzeBronze withwith aa NickelNickel InterlayerInterlayer GoldGold FilledFilled WireWire

„ HowHow isis itit manufactured?manufactured? „ StartStart byby makingmaking aa plate…….plate……. KaratKarat Gold,Gold, BrazingBrazing AlloyAlloy andand BaseBase MetalMetal DiskDisk ComponentsComponents (Top:(Top: afterafter )brazing) Left to Right: Bonded Disk, Rolled into Circle, Cut Circle DeepDeep--DrawnDrawn CupsCups (Gold(Gold SurfaceSurface Outside)Outside) StagesStages ofof DeepDeep DrawingDrawing ComponentsComponents ofof GoldGold FilledFilled WireWire BraceletsBracelets mademade fromfrom GoldGold FilledFilled PatternPattern WireWire GoldGold Filled,Filled, SolderSolder CoreCore WireWire Gold Filled, Wire with a Nickel Interlayer IntrinsicIntrinsic ValueValue

1414 KaratKarat Gold:Gold: 14/2414/24 xx 600600 == $$ 350/oz350/oz 1/201/20 1414 KtKt G.F.:G.F.: 1/201/20 xx 14/2414/24 xx 600600 == $$ 17.50/oz17.50/oz 1/201/20 1212 KtKt G.F.:G.F.: 1/201/20 xx 12/2412/24 xx 600600 == $$ 15.00/oz15.00/oz U.S.U.S. RegulationsRegulations forfor thethe JewelryJewelry IndustryIndustry

„ NationalNational GoldGold andand SilverSilver StampingStamping ActAct (amended(amended inin 19761976 withwith thethe GoldGold LabelingLabeling Act)Act) „ FederalFederal TradeTrade CommissionCommission GuidesGuides forfor thethe JewelryJewelry IndustryIndustry (1997(1997 revision),revision), thesethese guidesguides covercover industryindustry productsproducts mademade ofof preciousprecious metals,metals, ,diamonds, ,pearls, ,gemstones, watchcaseswatchcases andand watchbandswatchbands FTCFTC GuidesGuides

„ Gold:Gold: minimumminimum 1010 Kt,Kt, 33 pptppt tolerancetolerance „ Silver,Silver, SolidSolid Silver,Silver, SterlingSterling Silver:Silver: AtAt leastleast 92.5%92.5% AgAg (925/1000)(925/1000) „ CoinCoin Silver,Silver, 90.0%90.0% AgAg (900/1000)(900/1000) „ NickelNickel SilverSilver (German(German Silver)?Silver)? GoldGold FilledFilled

„ AA productproduct onon whichwhich therethere hashas beenbeen affixedaffixed aa platingplating ofof goldgold alloyalloy ofof notnot lessless thanthan 1010 KtKt finenessfineness „ PlatingPlating mustmust bebe atat leastleast 1/201/20 ofof thethe weightweight ofof thethe entireentire articlearticle „ PlatingPlating mustmust bebe affixedaffixed byby mechanicalmechanical meansmeans suchsuch asas ,soldering, brazing,brazing, weldingwelding MarkingMarking forfor GoldGold FilledFilled

1414 KtKt GoldGold FilledFilled 1414 KtKt G.F.G.F. 1414 KtKt GoldGold PlatePlate (d)(d) 1414 KtKt GoldGold OverlayOverlay 1414 KtKt R.G.P.R.G.P. RolledRolled GoldGold Plate,Plate, GoldGold Plate,Plate, GoldGold OverlayOverlay

„ SameSame asas GoldGold Filled,Filled, exceptexcept thethe specifiedspecified 1/201/20th byby weightweight „ StrictStrict markingmarking requirements:requirements: 1/401/40 1212 KtKt GoldGold PlatePlate 1/401/40 1212 KtKt R.G.P.R.G.P. 1/401/40 1212 KtKt GoldGold OverlayOverlay „ CannotCannot callcall itit GoldGold FilledFilled unlessunless thethe platingplating isis atat leastleast 1/201/20th byby weightweight GoldGold ElectroplateElectroplate

„ AffixAffix goldgold byby electrolyticelectrolytic processprocess „ NoNo lessless thanthan 1010 KtKt „ MinimumMinimum thicknessthickness equivalentequivalent toto 77 millionthsmillionths ofof anan inchinch (0.18(0.18 micrometers)micrometers) ofof finefine goldgold HeavyHeavy GoldGold ElectroplateElectroplate

„ AsAs before,before, exceptexcept coatingcoating withwith minimumminimum thicknessthickness 100100 millionthsmillionths ofof anan inchinch (2.5(2.5 micrometers)micrometers) VermeilVermeil

„ Base:Base: SterlingSterling SilverSilver „ MinimumMinimum goldgold thickness:thickness: 120120 millionthsmillionths ofof anan inchinch (3(3 micrometers)micrometers) „ GoldGold coatingcoating eithereither mechanicalmechanical oror electroplatedelectroplated GoldGold Flashed,Flashed, GoldGold WashedWashed

„ 1010 KtKt minimumminimum „ NoNo minimumminimum coatingcoating thicknessthickness requirementrequirement QualityQuality MarkingMarking

„ Trademark:Trademark: namename oror trademarktrademark ofof thethe manufacturer,manufacturer, importer,importer, oror sellerseller „ PlacePlace trademarktrademark adjacentadjacent toto qualityquality markmark „ However…….However……. SystemSystem isis difficultdifficult toto police!police! AndAnd inin thethe U.S.U.S. nono IndependentIndependent AssayingAssaying isis RequiredRequired

U.K.U.K. HallmarkHallmark SystemSystem U.K.U.K. HallmarkHallmark SystemSystem FinenessFineness inin thethe U.K.U.K. SterlingSterling SilverSilver

„ 92.5%92.5% AgAg minimumminimum „ Balance:Balance: mostmost commonlycommonly CopperCopper „ SolubilitySolubility „ Strength,Strength, FormabilityFormability „ AgeAge HardeningHardening „ RecyclabilityRecyclability „ Color,Color, LusterLuster „ PatinaPatina SilverSilver--CopperCopper PhasePhase DiagramDiagram

Sterling Composition MicrostructureMicrostructure ofof InvestmentInvestment CastCast SterlingSterling SilverSilver RingRing (x250)(x250) MicrostructureMicrostructure ofof ContinuousContinuous CastCast SterlingSterling SilverSilver Rod,Rod, 0.400”0.400” diameterdiameter (x250)(x250) MicrostructureMicrostructure ofof 0.010”0.010” thickthick SterlingSterling SilverSilver Strip,Strip, SolutionSolution TreatedTreated atat 765C765C (x250)(x250) SilverSilver--CopperCopper PhasePhase DiagramDiagram

Sterling Composition MicrostructureMicrostructure ofof 0.010”0.010” thickthick SterlingSterling SilverSilver Strip,Strip, SolutionSolution TreatedTreated atat 726C726C (x250)(x250) OxygenOxygen inin SilverSilver

SilverSilver OxideOxide isis unstableunstable atat T>455T>455 CC (851(851 F)F)

AtAt OneOne Atmosphere,Atmosphere, SolubilitySolubility ofof OO inin AgAg aboveabove m.p.=m.p.= 0.3%0.3% SolubilitySolubility ofof OO inin AgAg belowbelow m.p.=m.p.= 0.006%0.006% (50(50 timestimes less)less)

Thus,Thus, OO isis releasedreleased duringduring solidification!solidification!

“Spit”,“Spit”, ,Porosity, OxidesOxides ofof basebase metalsmetals DeoxidationDeoxidation ofof SilverSilver

CarbonCarbon Reduction:Reduction:

CC ++ OO == COCO Also,Also, cancan useuse scavengerscavenger inertinert gasgas (Ar)(Ar)

InIn silversilver // coppercopper alloys:alloys:

CC ++ CuCu2OO == 2Cu2Cu ++ COCO CC ++ CuOCuO == CuCu ++ COCO DeoxidationDeoxidation ofof SterlingSterling SilverSilver

„ AfterAfter carboncarbon reduction,reduction, addadd phosphorusphosphorus

„ GoodGood scavenger,scavenger, formsforms PP2OO5 ()(slag) „ SmallSmall amount,amount, ~~ 0.02%0.02% „ AddAdd asas “master“master alloy”:alloy”: 85%85% CuCu –– 15%15% PP ReticulationReticulation

„ TechniqueTechnique toto applyapply “texture”“texture” „ MeltMelt corecore ofof alloy,alloy, notnot thethe surfacesurface „ i.e.i.e. 80Ag80Ag--20Cu,20Cu, heatheat // chemicallychemically treatedtreated „ OxidizeOxidize thethe copper,copper, thenthen picklepickle „ SurfaceSurface richrich inin Ag,Ag, higherhigher meltingmelting pointpoint „ MuchMuch likelike depletiondepletion gilding!gilding! ReticulationReticulation ofof 80Ag80Ag--20Cu20Cu ReticulationReticulation ofof 80Ag80Ag--20Cu20Cu ReticulationReticulation ofof 1414 KtKt GoldGold ReticulationReticulation inin JewelryJewelry ReticulationReticulation inin JewelryJewelry FireFire StainStain oror FireFire ScaleScale

„ ResultsResults fromfrom annealingannealing oror heatheat treatingtreating silversilver // coppercopper alloysalloys (oxidation(oxidation ofof copper)copper) „ Tenacious,Tenacious, cancan bebe removedremoved byby picklingpickling „ DevelopmentDevelopment ofof “alternative”“alternative” SterlingSterling SilverSilver formulations,formulations, containingcontaining Zn,Zn, Sn,Sn, GeGe „ SomeSome claimclaim “anti“anti--tarnish”tarnish” „ MixedMixed Success…..Success….. „ “Traditional”“Traditional” Ag/CuAg/Cu worksworks !well! HeishiHeishi

„ AmericanAmerican IndianIndian JewelryJewelry „ HeishiHeishi:: TinyTiny beadsbeads fromfrom naturalnatural materials,materials, handhand mademade intointo preciseprecise sizessizes withwith aa holehole soso theythey cancan bebe strungstrung intointo necklacesnecklaces „ SilverSilver HeishiHeishi ,Beads, oror liquidliquid silversilver beadsbeads „ MadeMade fromfrom silversilver stripstrip HeishiHeishi NecklaceNecklace ContrastingContrasting Application:Application: VeryVery LargeLarge SilverSilver TubesTubes CastCast // MachinedMachined SilverSilver BilletBillet CastCast // MachinedMachined // EtchedEtched SilverSilver BilletsBillets TubeTube DrawingDrawing TubeTube DrawingDrawing SilverSilver Tube,Tube, 3.5”3.5” diameterdiameter SilverSilver TubingTubing EmbrittlementEmbrittlement ofof AncientAncient SilverSilver

„ R.J.HR.J.H Wanhill,Wanhill, EmbrittlementEmbrittlement ofof AncientAncient SilverSilver,, JournalJournal ofof FailureFailure AnalysisAnalysis andand Prevention,Prevention, VolumeVolume 55 (1),(1), FebruaryFebruary 20052005 „ CausesCauses ofof Embrittlement:Embrittlement: „ CorrosionCorrosion InducedInduced „ MicrostructurallyMicrostructurally InducedInduced „ SynergisticSynergistic effecteffect „ KnowledgeKnowledge == RestorationRestoration andand ConservationConservation EmbrittlementEmbrittlement ofof AncientAncient SilverSilver (Cont.)(Cont.)

„ IntergranularIntergranular CorrosionCorrosion,, typicaltypical ofof mechanicallymechanically workedworked // annealedannealed objectsobjects

„ InterdendriticInterdendritic CorrosionCorrosion,, duedue toto coppercopper segregationsegregation uponupon solidificationsolidification EmbrittlementEmbrittlement ofof AncientAncient SilverSilver (Cont.)(Cont.)

„ MicrostructurallyMicrostructurally InducedInduced EmbrittlementEmbrittlement,, intergranularintergranular fracturefracture duedue toto impurityimpurity elementselements (Pb,(Pb, Bi)Bi) segregatingsegregating toto graingrain boundariesboundaries EmbrittlementEmbrittlement ofof AncientAncient SilverSilver (Cont.)(Cont.)

GundestrupGundestrup CauldronCauldron „ 22nd oror 11st centurycentury B.C.B.C. „ MetallographyMetallography „ FieldField EmissionEmission SEMSEM „ ElectronElectron BackscatterBackscatter DiffractionDiffraction EmbrittlementEmbrittlement ofof AncientAncient SilverSilver (Cont.)(Cont.)

„ Annealed,Annealed, freefree ofof corrosioncorrosion „ RemanentRemanent coldcold deformation,deformation, corrosioncorrosion damagedamage „ ConclusionConclusion:: coldcold deformationdeformation waswas primarilyprimarily responsibleresponsible forfor corrosioncorrosion EmbrittlementEmbrittlement ofof AncientAncient SilverSilver (Cont.)(Cont.)

EgyptianEgyptian VaseVase „ PtolemaicPtolemaic Period,Period, betweenbetween 300300 andand 200200 B.C.B.C. „ MetallographyMetallography „ SEMSEM „ EDX:EDX: 97.1%Ag,97.1%Ag, 0.9%Cu,0.9%Cu, 0.7%Pb,0.7%Pb, 0.3%Sb0.3%Sb EmbrittlementEmbrittlement ofof AncientAncient SilverSilver (Cont.)(Cont.)

„ CorrosionCorrosion alongalong slipslip lineslines (deformation)(deformation) „ LinkLink betweenbetween remnantremnant coldcold deformationdeformation andand corrosioncorrosion damagedamage „ MicrostructurallyMicrostructurally-- inducedinduced embrittlement,embrittlement, 0.7%Pb0.7%Pb „ SynergisticSynergistic effecteffect EmbrittlementEmbrittlement ofof AncientAncient SilverSilver (Cont.)(Cont.)

ByzantineByzantine PatenPaten „ CircaCirca 600600 A.D.A.D. „ ExtensiveExtensive breakagebreakage alongalong annularannular decoratingdecorating groovesgrooves EmbrittlementEmbrittlement ofof AncientAncient SilverSilver (Cont.)(Cont.)

„ IntergranularIntergranular corrosioncorrosion atat surfacesurface „ CopperCopper precipitationprecipitation atat graingrain boundariesboundaries „ Conclusion:Conclusion: preferentialpreferential corrosioncorrosion alongalong decoratingdecorating ,grooves, thusthus mostmost corrosioncorrosion waswas duedue toto remanentremanent coldcold deformationdeformation EmbrittlementEmbrittlement ofof AncientAncient SilverSilver (Cont.)(Cont.)

RemedialRemedial MeasuresMeasures (reversible?)(reversible?) „ CorrosionCorrosion ProtectionProtection „ Cleaning (hydrogen reduction, reduces corrosion products to metallic silver) „ Outgassing (dry the moisture) „ Protective coatings (-type are very thin and uniform) „ HeatHeat TreatmentTreatment „ Relatively high temperature „ Risk of incipient melting „ Problem with soldered joints, inlays, etc. „ Irreversible PlatinumPlatinum GroupGroup MetalsMetals (PGM)(PGM)

„ PlatinumPlatinum „ PalladiumPalladium „ IridiumIridium „ RutheniumRuthenium „ RhodiumRhodium „ OsmiumOsmium PlatinumPlatinum

„ 950/1000950/1000 purepure Pt:Pt: PlatinumPlatinum „ 950/1000950/1000 PGM,PGM, 750/1000750/1000 Pt:Pt: i.e.i.e. IrIr--PtPt „ 950/1000950/1000 PGM,PGM, 500/1000500/1000 Pt:Pt: i.e.i.e. 600Pt600Pt--300Ir300Ir--100Pd100Pd CommonCommon PlatinumPlatinum AlloysAlloys

„ PtPt--5%5% RuRu „ PtPt--5%5% IrIr „ PtPt--5%5% PdPd „ PtPt--5%5% CoCo „ PtPt--10%10% IrIr

AllAll areare “harder”“harder” thanthan purepure platinumplatinum MeltingMelting ofof PlatinumPlatinum

„ VeryVery highhigh MeltingMelting Point:Point: 32143214 FF (1768(1768 C)C) „ VeryVery reactivereactive whenwhen molten.molten. KeepKeep Clean!Clean! „ MustMust bebe degasseddegassed „ ScrapScrap accountability!accountability!

IfIf youyou dodo everythingeverything right……….right………. PlatinumPlatinum TubingTubing TheThe End!End!

„ OverviewOverview ofof PreciousPrecious MetalsMetals „ MetallurgyMetallurgy „ TouchedTouched onon somesome relevantrelevant topicstopics „ ExpandExpand knowledge!knowledge! „ MyMy ee--mail:mail: [email protected]@alum.mit.edu AcknowledgementsAcknowledgements

„ WorldWorld GoldGold CouncilCouncil „ SantaSanta FeFe SymposiumSymposium „ HallmarkingHallmarking OfficeOffice „ LeachLeach && GarnerGarner „ HooverHoover andand StrongStrong „ CiminiCimini && AssociatesAssociates