ZincSurfaces
inArchitectureandArt
L.WilliamZahner
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LibraryofCongressCataloging-in-PublicationData
Names:Zahner,L.William,author.|JohnWiley&Sons,publisher.
Title:Zincsurfaces:aguidetoalloys,finishes,fabrication,and maintenanceinarchitectureandart/L.WilliamZahner.
Othertitles:Zahner’sarchitecturalmetalsseries
Description:Hoboken,NewJersey:Wiley,[2021]|Series:Zahner’s ArchitecturalMetalsSeries
Identifiers:LCCN2021003278(print)|LCCN2021003279(ebook)|ISBN 9781119541615(paperback)|ISBN9781119541639(adobepdf)|ISBN 9781119541592(epub)
Subjects:LCSH:Zinc—Surfaces.|Zinc—Finishing.|Zinccoatings.| Architecturalmetal-work.|Artmetal-work.
Classification:LCCTS640.Z342021(print)|LCCTS640(ebook)|DDC 661/.0661—dc23
LCrecordavailableathttps://lccn.loc.gov/2021003278
LCebookrecordavailableathttps://lccn.loc.gov/2021003279
CoverDesign:Wiley
CoverImages:(Main) StevenHollArchitects’,InstituteforContemporaryArt(ICA),VirginiaCommonwealth University,photographedbyIwanBann,c.2017.(Border) Patternonzincplates ©somnuk/GettyImages
10987654321
ThisbookisdedicatedtomygoodfriendVerneChristensen. (adesignerwhoprovedAlessandroVolta’stheorywhenwebuiltabeautifulcurvedzincroofbelowhis coppergutters)
PreweatheredZincSurface73
ClearCoatingwithPigmentation77 BlackenedZinc77
CustomPatinaFinish79
DarkVariegatedPatinasonZinc80
ZincOxidePatinas87
ZincIridescentPatina93
GalvanizedZincSurfaces93
GalvanizedSteelStructuralShapes99
DarkeningGalvanizedSteel100
ZincPhosphateCoatingsonGalvanizedSteel101
ZincFabric102
OtherMethodsofApplyingZinctoSteel103
ZincAnodizing104
CHAPTER4Expectations105
CHAPTER7Corrosion215
Introduction215
ZincasaProtectiveCoating216
GalvanizedSteel218
ZincAlloyCoatingsonSteel219
ZincPowderinPaintCoatings220
Sherardizing221
ThermalSpray221
ZincAnodes222
Battery222
WhenZincDoesNotProtectSteel224
ZincCorrosion225
InteriorExposures227
ExteriorExposures228
ShelteredExteriorSurfaces230
UniformCorrosion235
UndersideCorrosion236
WetStorageStain237
GalvanicCorrosion239
DeterminingFactorsforGalvanicCorrosion242
DifferenceinElectro-Potential243
GeometricRelationship243
Distance244
ElectrolyteEffects244
TemperatureEffects245
PittingCorrosion246
IntergranularCorrosion248
StressCorrosionCracking248
ZincArtifactsandStatues249
DeicingSalts251
Chlorides252
Fertilizer253
Saponification254
CorrosiveSubstancesinProximity254
CHAPTER8MaintainingtheZincSurface257
Introduction257
ZincSurfaces258
WhyaMaintenanceProcedure260
DevelopaMaintenanceStrategy260
RestoringthePreweatheredAppearance264
EffectsofDifferentEnvironments266
Preface
Anexpertisanordinarymanwho-whenheisnothome–givesadvice. OscarWilde Zincisthemysteriousmetalusedinartandarchitecture.
IntheUnitedStates,itisaparadox.Ontheonehand,itisconsideredanOldWorldmetal, usedforcenturiesacrossEurope.Parisisdefinedbytheroofsofzincthatblanketthecity.Yetitis relativelynewtoNorthAmericanarchitecture.
Asametalofartcastingorfenestration,littlewasknownuntiltheearly1990s.Sure,weknew oftheprocessofdippingsteelinamoltenjacketofzinc.Hot-dippedgalvanized,astrangefondue formetal,isaprocessthatiswellknown,butnotalwaysunderstood.
TheleadingzincminesthatsuppliedtheworldwereonceinthemiddleoftheUnitedStates, aregionwiththetownofJoplin,Missouri,asthecenter.Mostzincmininghasendedinthearea, butinthelate1800sandearly1900sthiswastheepicenterofzinc.Millionairesweremadebythe dozensastheareawastunneledoutlikeagiantanthill.
InNorthAmerica,thesheetmetalindustry,artcastingindustry,anddesigncommunityknew littleaboutzinc.Publicationsandtrainingdocumentsthroughoutthearchitecturalmetalindustry madenomentionofzinc.Theoldcatalogscalledthemetal whitebronze, perhapsattemptingto elicitafeelingofnoteworthinessbytakingonthename bronze.Metalfoundries,artschools,and metalworkersintheUnitedStateslackedanyrealknowledgeofthemetal.Withtheexceptionof galvanizing,themetalwasallbutforgottenaftertheearlypartofthetwentiethcentury.
WhenIfirststartedworkatZahner,a125-year-oldmetalfabricationcompanylocatedinthe Midwest,zincwasnotknownasanarchitecturalmetal.Wedidnotstockthemetal,norwasitspecifiedinanyindustrypublications.Weworkedwithsteel,terne,copper,aluminum,stainlesssteel, andlead,butnotzinc.Oneofthefirstintroductionstothemetaloccurredduringtherestoration oftheFollyTheater,aturn-of-the-centurytheaterbuiltin1900.Whentheworkersremovedpartsof themetalcorniceanddecorativemetalbalusterin1979,theyhaddifficultydeterminingwhatthe metalwas.Thismetalhadlasted80yearsandstilllookedingoodshape.Itwassilverunderthe paint,soitwasnotcopper.Itwasnotmagneticsoitwasnotterne-platedsteelorgalvanizedsteel. Itwasheavy,soitwasn’taluminum,andaluminumhadnotbeenincommonuseby1900.The pieceswerespunandassembledinsectionsbysoldering.Itwasnotanymetalwewerefamiliar with.Itwaszinc.Fromthe oldcountry.
Theotherconnectiontozincgoesback125years.AndrewZahner,mygreatgrandfather,started thismetalcompanyIworkfor,inJoplin,Missouri,in1897.Backinthelate1800s,thisregionin
southwesternMissouri,ontheedgeoftheOzarkMountains,wasthesiteofoneofthelargestmining operationsinAmerica–firstforleadusedtomakebulletsandlaterforzinc.Zinc,knowninthearea as jack, madetheregiononeofthewealthiestintheUnitedStates.Everymajorrailroadatthe timewentthroughtheJoplinregiontotransporttheorearoundtheUnitedStatesandtoportsto supplytheEuropeanmarket.TheorewasofsuchhighqualitythattheEuropeanspurchaseditfrom Missouri.
ThisboomingregionattractedayoungAndrewZahner,andhestartedasmallmetalfabrication firmtoproducecornicesandotherdecorativefeaturesforthewealthymerchantsinthearea.
AndrewZahnersurelyknewaboutzinc.
Theboom/bustcycleeventuallyhittheJoplinareaintheearly1900s,andAndrewmoved thecompanytoitscurrenthomeinKansasCity.Theknowledgeofzincwasleftbehindwiththe dyingminesofthecentralUnitedStates.Now,125yearslater,Iwriteabookonthismetal,zinc. ItisunfortunatethatIdidnothaveAndrewasaresource.
Overthelastcoupleofdecades,wehaveworkedwiththemetalzinconnumerousprojects.We haveexpandedourknowledgeofthemetalandhaveuncoveredmanynewandinterestingwaysof workingwithzinc.Wehavecreatednewpatinasandsurfaceenhancements,andwehaveexplored casting.ThemoreIworkwiththemetalzinc,themoreIfinditanintriguingmaterialofdesign.
WorkingwithmydaughterKat,whooperatesZahnerMetalConservation,restoring100-yearoldzincstatuesandstatuettesgivesadeepappreciationforhowtheartistworkedwiththemetal andproducedamazingdetailusingcastingtechniquesthathaveallbeenforgotten.
Thisbook,thefifthintheseriesonmetals,isintendedtosparktheinterestinthemetalzinc andexplorethepossibilitiesithastoofferthedesignerandtheartist.Thenextpagesshouldhelp tounravelthisinterestingmaterialofdesignandintroducethereadertohowthismetalwillappear andfunction.
L.WilliamZahner
IntroductiontoZinc
It’sabusiness.IfIcouldmakemoremoneydowninthezincmines,I’dbe miningzinc
Source:RogerMaris
ELEMENT30ZN– SPELTER
Zinc,themetalthatcouldchangecopperintogold,atleastthatwasthewishoftheearlyalchemists. Theycalledthemetal counterfeht1 .Itlookedlikesilver,butitwasn’t.Addingittomoltencopper andthecopperwouldturntoabeautifulgoldencolor,butitwasnotgold.Itwasan“imitation” a counterfeht.Thisoddmetal,ifitwasametalatall,wasamystery.
Zincwentalsobythename spelter, usedmainlybythosewhoworkedwiththemetal.Spelter waspossiblyacorruptionofthenamefor“pewter,”thedullgray,lead-tinalloy.TheDutch,first toimportthemetalintoEuropeusedtheword, spiauter forawordtodescribeamixtureoflead andtin2 .So,itverywellmayhavebeenanearlymarketingploytogivevaluetothisdubiousmetal. Spelterwasthenamegiventothismetalupuntilrelativelyrecenttimes.Today,thenamezinchas firmlytakenholdontheperiodictableofelements.
Othernames,inparticular calamine, werefrequentlyusedforthismetalbeforeitwasofficially ametal.Calamine,theprincipalmineralofzinc,wasthenameusedacrossWesterncivilizations sincethetimeoftheRomans.Calamineiszincsulfide,andthereareregionsinEuropewherethe richmineraldepositsofzincsulfideweremined.
Calamine,aswell,lostoutasanamefortheprincipalmineralformofzincandisnowbetter knownasthepopulartopicalpoisonivycream,eventhoughthelotioncontainszincoxide,notthe
1 TheGerman,GeorgiusAgricola,inhisbook, Deremetallica,writtenin1556.
2 DawkinsJ.M., ZincandSpelter, 1950,ZincDevelopmentAssociation,p.24.
zincsulfideofthemineralform.Insteadofcalamine,theterm sphalerite isusedasthenameforthe zincsulfidemineral.Foralongwhiletheterm zincblende, fromtheGerman zincblende,wasalso usedtodescribethemineral.Confusionreignedonwhatthismineralormetalactuallywas.
Asametal,zincinawroughtorcastformcamelate,sometimeinthemiddleofthesixteenth centurytotheWesterncivilizations,definitelyearlierinIndia.Chinaalsowasanearlyzincproducer,usingcrucibleswithcharcoaltoheattheore.Theymadecoinsfromzincinthefourteenth century.TheRomanswouldproducebrassfromcopperbyaddingcalamineandheatingitinsmall crucibles.Thezincwasobtainedbyreducingtheore,releasingcarbondioxide,andthefumesofzinc wouldrapidlybeabsorbedintothecopper.Oncemelted,theslag-coveredblockwouldbehammered andthebrightyellowcolorwouldappear.
Theprocessofmakingbrasswaswellknownthroughoutantiquity.Themethodofcreatingbrass fromsphalerite(orcalamine,asitwasthenknown)wasdescribedinseveraltexts.Onesuchtext, SchedulaDiversariumArtium,writtenbyTheophilusPresbyterintheeleventhcentury,describes theheatingofcruciblesinanopenfurnace,addingcalamine,thenstripsofcopper.Placebackon thefurnacefor9hoursandyouarriveatagoldenyellowcolorpleasingtolookat.Figure1.1shows themineralsphaleritewithalargelumpofcopperonaplateofbrass.
Zincappearedasaknownmetallaterthanleadandtin.Themineralwasknownbutasadistinct metal,zincwasnot.Alongwithothercolorfulzincminerals,sphaleritewaseasytoidentifyandso wasminedinantiquityasamineraltoaddtocoppertoproducethebeautifulyellowbrass.Granted, itwasoftenmistakenforgalena,aleadsulfidemineral,atonetimeavaluablemineralformaking bullets.
EarlybrassartifactsdatingbacktotheeighthcenturyBCEwereuncoveredintheGordiontomb excavatedinAnatolia.Thecopper–zincmetalwascalled oreichalkos andlater orichalcum bythe Romans.Theprocessofproducingbrasswaswellknownanddocumented.Mostbrassproduction wasestablishednearthezincminesbecauseitwaseasiertocartcoppertothearea,thanthelarge quantityofzincmineralneeded.
FIGURE1.1 Sphaleritepluscoppertomakebrass.
Thereasonzincasaknownmetalwaslatetodiscoveryisthedifficultyofrefinement.Upuntil themid-1700s,metalsweremadebyroastingtheoresandburningofftheoxidestofreethemetal. Troubleis,zinchasalowboilingpointasmetalsgo.Assufficientheatisappliedtoreducetheore, zincturnstogasandthefumesescape.Thus,thereductionoftheorethewayothermetalsare producedjustdidnotworkforzinc.
Thewaytheearlyalchemistsfoundthis counterfeht,itwouldcondenseonthewallsoftheflue andincracksandcrevicesofthestoneafterroastingmetaloresthatcontainedzinc.Zincisoften foundinoresofothermetals,particularlylead,copperandsilver.Whentheoreswereheatedthe zincwouldgoupasvaporsandcondenseonthestone.Whenitcondensed,itformedlong,whiskery tuffsthealchemistscalled lanaphilosophica, meaning“philosopher’swool.”
Assistantstothealchemistswouldscrapeandcollectthiswoolysubstanceoffthestoneandout ofthecracksofthefluewalls.Thealchemistsplacedavalueonthisspecialmetalthatwasliketin butwhenaddedtocopperwouldtransformthecopperintoagoldenyellow.
Alchemistsymbolforzinc.
Zincisasilvermetalwithaslightbluishhue.Zinccanbepolishedtoabright,silverbutquickly tarnisheswhenhandled.Aszincagesitturnstoarichgraycolorwithwhitishoxidesinareaswhere moistureisallowedtoaccumulate.
Zinciselement30ontheperiodictableofelements,Figure1.2.Withtheredmetal,copper,on onesideandgallium,abluegraymetalthatmeltsinyourhand,ontheother,zincfallsinthetwelfth rowwithcadmiumandmercury.
Zinchasseveralisotopes,buttheisotopezinc67isratherspecial.Zinc67occursinapproximately4%ofnaturalzinc.Thisisotopeishighlysensitivetominutevariationsintransmittedenergy. Whenitdetectsenergy,itemitselectromagneticradiationmakingthisisotopezinc67valuablefor highaccuracymeasuringequipment.Zinc67isusedtodetectgammarayvibrationswithincredible sensitivityinthehighlyaccurateatomicclock.
Zinchasahexagonalcrystalstructure,whicheventhoughitiscloselypacked,itislessdense thanthecubicstructureofironorcopper.Figure1.3.depictsacloselypackedhexagonalcrystal. Thismetallurgicalstructureshowsthecrystalofzinchassixatomsinanearplaneandanother sixslightlyfurtheraway.Thismakesthebondsofthebasalplaneslightlystrongerthanthebondsof theparallelplane.Thisdifferenceindistanceandstrengthgiveszincananisotropythattranslates toformsmadeofzinc.3
3 Porter,Frank, ZincHandbook,MarcelDeckerInc.,NY,p.45.
FIGURE1.2 Periodictable.
VIIIA
Anotheraspectofzincisitsabilitytorecrystallizerapidlyafterdeformation.Thispreventswork hardeningfromoccurringduringformingoperationsanditalsoprovidesalevelof“self-lubrication” asthecrystalsslipoveroneanotherduringformingprocesses.
Note,thespanglethatformsongalvanizedsteelisalargecrystalofzincthatformsasitcools. Ithasthesixtriangularwedge-likesymmetryreflectingthehexagonalcrystalstructureofthezinc crystallattice.Figure1.4showsaclose-upimageofthespangleformedwhenzinccoolsonasteel
FIGURE1.3 Zinchexagonalcrystalstructure.
FIGURE1.4 Spangleofgalvanized.
FIGURE1.5 Zinccoatingonsteelusingacontrolledrefinementofthecoolingprocess.
substrate.Thewedgesthatexpandoutfromacentralpointarecalleddendritesandtheparallellines arecalledsubdendrites.Whennewlydevelopedthegalvanizedsurfacehasacrystallinereflective qualityduetothewaythesubdendritesscatterthereflectivelight.Thesurfaceseemstocomealive asyouwalkaroundanewlygalvanizedsteelplatewiththeglitteringreflectionbouncingoffthe variationsinthecrystals.
Thisreflectiveness,achievedbyhot-dippingsteelintomoltenzinc,isanaturalsurfacethat formsduetoslightimperfectionsinthezincbathorslightroughnessonthesteelsurface.These imperfectionsinitiatetheformationofthedendritegrowth.
Artisticaffectscanbeenhancedtotakeadvantageofcoolingratesofthemoltenzinc.Thesetechniquesarestillindevelopmentinordertobetterunderstandingtheparametersinvolved.However, coolingrates,“seeding”themoltenbathwithotherelementscaninfluencetheeffects.
Thedifficultyarisesintheindustrialcontrolsinplacebythegalvanizingfacilities.Artistic expressionisnotintheirnormalparlance.
Figure1.5showsa“wave-like”appearancethathasdevelopedonflatsteelsheet.Thereflectivity enhancesthethree-dimensionalappearanceofthezincsurface.
Asthesurfaceoxidizes,thezinccrystalsstillvaryinappearancecreatingadull,lowerreflective patchworkappearance.Thedendritesarestillthere,theyhavejustdevelopedalayerofzinc oxidethatmutesthereflectivity.Figure1.6showsagalvanizedplatethathasbeenexposed toweather.
FIGURE1.6 Galvanizedthathasweathered.
ZincELEMENT30
Atomicnumber30
Crystalstructure: Close-packedhexagonal
Mainmineralsource: Sphalerite(Calamine)
Color: Bluishwhite
Oxide: White
Density: 7,068kg/m3
Specificgravity: 7.0
Meltingpoint: 419∘ C
Thermalconductivity: 112W/m ∘ C
Coefficientoflinearexpansion: 19 × 10-6 m/m∘ C
Electricalconductivity: 26%IACS
Modulusofelasticity: 108GPa
MostofthezincfoundontheEarth’ssurfaceisfromhydrothermalactivitythatbrought themetaltoornearthesurface.Zincisnotfoundinthenativestate.Zincisalwaysfoundin combinationwithotherelementsandmetals.Zincisthe24th mostabundantelementwithinthe uppercrustoftheEarth.
Zinchasapoorstrengthtoweightratioascomparedtoothermetalsusedinindustry.
Zincalloysareductileatroomtemperature.Zinccastingsarenotductile.
Zincissubjecttofracturewhenformedatlowtemperatures.
Highelasticity–resiliencyundershockloading
Softedge
Zincandzincoxidesarenontoxicunlessconsumedinlargeamounts.Zincoxidefumesare hazardouswheninhaledandwillcauseflu-likesymptomsthatcanlast1–2days.
Ithassuperiorcorrosionresistanceinmanynaturalenvironments.ZincissubjecttocorrosioninlowpHandhighpHenvironments.
FINISHES:
Millfinish–asrolled. Semi-bright
Preweathered–darkened
Zinccanbepainted.
Coil-coatedzincsheetinvariouscolorsareavailableonthemarket. Oil-basedpaintsarenotrecommended.Saponificationcandevelop.
Platingwithothermetalssuchascopper,silver,nickel,andgoldarepossible.
Artificialpatina:
Brightappearance:
Reflectanceofultraviolet: ofinfrared:
Zinccanreceiveartificialpatinasofwhite,black, browns,mottledbrownswithgreenandreddish oxidesaswellasiredescenthuesoftransparent greens,purplesandreds.
Zinccanbepolishedbutthelusterquicklydiminishes asoxidesform.Thecoloristypicallyamattegrayto grayishblue.
Theoxideofzincabsorbsultravioletlight.Itsusein sunprotectioniswellknown.Protectionisafforded byabsorptionoftheultravioletradiationandnot allowingittopasstotheskin.
Zincoxideinpowderformisusedextensivelyinpaint. Itisawhitepowderandwillreflectinfraredradiation.
Relativecost: Medium
Strengthening:
Recycleability:
Zincdoesnotgainstrengthfromcoldworkingas othermetalsdo.Instead,alloyingwithsmallamounts ofcopperandtitaniumareusedtoimprovestrength andaddcreepresistance.
Zinciseasilyrecycledbecauseofthelowmelting point.Zinciscapturedinfromgalvanizecoatedsteels asvaporduringtherecyclingprocessofcoatedsteels.
Weldingandjoining: Zinccanbeweldedandsoldered.
Casting:
Zincisacommoncastingmetal.Usedformanysmall castpartswherestrengthislessarequirement
Plating: Zinccanbeelectroplatedwithothermetals.
Etchingandmilling:
THEZINCATOM
Zinccanbeetchedchemicallyandreadilymachined.
Allmetalshaveatmostthreeelectronsintheiroutershell.Zinc,element30ontheperiodicchart, hastwoelectronsintheoutershell.Thisgivesitanoxidationstateof +2,makingthezincatom divalentinallcompounds.Figure1.7depictsatypicalzincatomwiththetwoelectronsintheouter orbitshell.Forzinc,thereisalwaystwocovalentbondsformedwhenthezincatomcombineswith otherelements.
OxygenreadilyjoinswithzinctoformZnOandZn(OH)2,withoxygenalonemakingadouble bondandthetwohydroxidecombinationseachwithasinglebond.
30 Protons
35 Neutrons
30 Electrons
Outer shell holds two electrons
FIGURE1.7 Zincatomwithtwoelectronsintheothershell.
High-purityzincisastrongoxidizerandwhenexposedtotheatmospherequicklytarnishes andformstheoxideandhydroxide.Thestandardpotentialofzinccanbeexpressedthermodynamically4 as:
Zn↔Zn2+ + 2e E0 = –0.763 v
Thisrepresentsastrongdrivetocombinewithotherelements.
4 Zhang,Z.G.CorrosionandElectrochemistryofZinc.PlenumPress,NY,1996.
HISTORY
ThediscoveryofzincasametaliscreditedintheWesttotheSwissalchemist,Paracelsus.Dr.Paracelsus,ashewasknownbecausehewasaphysicianandaphilosopheraswell,in1526,describeda metalhecalled zinek, asoneofthesevenknownmetals.ParacelsuslivedaroundBaselandwrote extensivelyonvarioussubjects.Heiscredited,amongotherthings,asthefatheroftoxicology.
ZincorewasminedinGermanyforthemakingofbrassintheregionaroundtheHarz Mountains.ThenearbytownofGoslar,Germany,wasacenterofminingandzincminingexisted fromaround1550.By1650,alarge-scalezincoreproductionandrefinementwasunderway. Theminesaroundthisregionproducediron,silver,copper,lead,andzinc.
Theprocessofrefiningthemetalstillwasamysterytothewest.ChinaandIndiawouldsupply themetalinarefinedstatetoEuropeancompaniesforproducingbrassbyalloyingwithcopper. Eventually,bythemiddlepartoftheeighteenthcentury,zinc-miningoperationsinSwedenandthe regionaroundSilesiawouldbecomeimportantsourcesfortheore.
Intheearly1700s,Bristol,England,theBristolBrassCompanywouldimportzincfromIndia. WilliamChampion,thesonofthefounderofthecompany,createdamethodofsmeltinghisown zincusingaprocessnotablysimilartoonedevelopedcenturiesearlierinIndia.Thecompanypreviouslywouldimportthezinctomakeitsbrassplates,nowitcouldproduceandrefineitsownzinc fromore.WilliamChampionhasbeencreditedwiththeearlymanufactureofindustrialquantities ofzinc.
ChampionsawhowthemetalworkersinIndiawereextractingzincfromtheorepyrometallurgicallybyaddingadistillationprocesstocapturethefumesandcondensethezincoxide.Thezinc washeatedtoturnitintovapor,thevaporwouldcondenseonthecoolerwallsofachambersimilar tothewayitwouldcondenseonthecoolerstonewallsofthealchemistsflue.Thiscondensedzinc waszincoxide.Thekeywastoremovetheoxygenbyaddingcharcoaltotheheatedchamberand thiswouldremovetheoxygenfromthezincoxidecreatingcarbondioxideandleavingthezincasa lumpofmetal.
Inthosedays,brasswasthemainproductthatsetthedemandforzinc.Brasswasusedtoclad thehullsofEnglishsailingships.Muntzmetal,analloyofcopperandzinc,contains40%zinc. Developedspecificallyasacladdingforshiphullsin1832,Muntz,namedafteritsinventor,George FredrickMuntzofBirmingham,England,replacedcopperasananti-foulingcladdingonthehulls ofoceangoingships.Becauseithadzinc,itwassignificantlycheaperthanpurecopperandstill wouldprotectthewoodhullsfromteredoshipworms.Muntzmetalwasalsomuchstrongerthan copper,andthezincloweredthemeltingpointto904∘ Cfrom1085∘ Cforcopper.
Zincisametalthathasbeeninandoutofartandarchitectureovertheyears.Sinceitsdiscovery,ormoreso,sincethetimewhencastingandrollingintosheets,zinchasfounduseinarchitecture.TheskylineofParisisatestimonytothebeautyanddurabilityofthemetal.Napoleon, around1805instructedthechemistJean-JacquesDonytodeveloptherichminesofzincoreinthe Vielle-Montagne.Donydevelopedamethodofrefiningtheoreusingahorizontaldistillingprocess thatinvolvedaseriesofretortssetintoafurnace.Theorewouldberoasted,andthezincfumeswould bereleasedandcondensate,formingmoltenzinc.Figure1.8isadiagrammaticrepresentationofthe retortprocess.
DiagramofaHorizontalRetort.
Source:DevelopedbyDony.
Donysettheseretortsinserieswithinafurnaceandrequiredavastamountofheatenergy.The processremainedinuseuntilthefirsthalfofthetwentiethcentury.First,thereactionrequiredthe temperaturewithintheretorttoreach1100∘ Corgreaterforthechemicalreactiontooccurbetween ZnOandcarbon.Thecarbonwasintroducedfromthecharcoal,whichwouldburn,creatingcarbon dioxidegas.Furtherheatwouldbeappliedtovaporizethezinc.Zincoxidewouldformasavapor, andwhenitcombinedwiththeheatedcarbon,theoxygenwouldbestrippedawayandventoutas carbondioxide.Thezincwouldbecondensingonthecoolerportionoftheretortandcollectalong thebottomasliquidmetal.
Theseretortswouldbesetintoarraysandchargedwithoreandcharcoal.
Withthisnewsourceofthemetal,rollingintosheetsandplateswaspossibleusingrolling techniquesperfectedwithcopperandironplates.Thefirstzinc-rollingmillforsheetsofzincwas developedbyDonyin1812,makingthismetalavailableasanarchitecturalcladdingmaterialto competewithcopperandtin-platedsteel.
Zinchasalonghistoryinartandarchitecture.Itsuseasanalloymetalwithcoppertomake brasswaswellunderstoodbytheRomansandEgyptians,whowereattractedbytheallureofthe goldencolortheadditionofthemineralcalaminemadewithcopper.Atleasttheyunderstoodthat somethingintheorewouldinteractwithcopperandproducebrass.Zincasametalwasunknown toearlycivilizationsbecauseitcouldnotbeseparatedfromitsoreasothermetals.Whencopper, lead,tin,orironorewereheatedthemetalwouldfalltothebottomofthefurnacebutzincwould boilandturntovapor.
InChinaandinIndia,earlymetalworkersfoundwaysofisolatingzincbyroastingtheoresin crucibleswithcharcoalandthenallowingthemtocool.Zincwouldseparateinsmalllumpswhere itcouldbecollectedandremelted.
FIGURE1.8
FIGURE1.9 AnexampleofmodernBidriwaremadefromzinc.
Inthefourteenthcentury,therewasanartformcalledBidrithatusedhammeredcopperand zincformswithincredibleinlayartwork.Figure1.9isamodernexampleoftheartwork.Bidriisa productthatoriginatedinsouthcentralIndiaandisattributedtotheBahamanisultansinthefort cityofBidar.Theyusedtheprocessofengravingandrepossétoproduceelaboratedesignsinmetal bowlsandplatesaswellasthebasesofhookahs.
Theywouldofteninlayothermetalssuchassilverorgoldandthendarkenthebackground metalwithsulfidecompoundsandpolishoffthetopsections.
ThisareaofIndiaisstillamajorcenterformanufacturinguniquemetalwork.Today,brass, copper,andzincarestillhandcraftedhereintheoldtradition.Itisimportanttonote,theseincredible artpieceswerecreatedfromzinc–copperalloys,wherethezincwas4timestheamountofcopper inthebasemetaltoasmuchas16times.ZincwasbeingproducedinlargequantitiesinIndiaas earlyasthefourteenthcentury.
TherewasnoknownprocessofproducingzincinEuropeuntilseveralcenturieslater.In1982, anarcheologicalstudyoftheminesintheregionaroundZawarinRajasthanwasundertakenbya British-Indianresearchgroup.Theyfoundintactfurnacesandclayretortsthatindicatedsmeltingof zinconasignificantscalehadbeenunderwaycenturiesago5 .Theclayretortswerepositionedatan angle.Theneck-downareawaslowerthantheenlargedsectionandpositionedthroughawallofclay andstoneintoacoolerchamber–muchthesamewayasWilliamChampionandJean-JacquesDony arrangedtheirretortstocapturezincvaporandcondenseittocreateapureformofzinc.William ChampiontraveledoftentoIndia,andapparentlyhestudiedtheIndianprocessandbroughtitback toEngland.
5 JagdishMittal, BidriWareandDamasceneWorkinJagdishandKamlaMittalMuseumofIndianArt,Hyderabad, 2011,p.39.
OtherexamplesofzincusedinthefarEasternculturespredatethearrivalofthemetaltoEurope. Zincwasrarerthancopperandironintheseearlytimes,andtheutilityofthemetalwasnotyet understooduntillargerquantitiescouldbeproduced.
InEurope,oncemoreintenserefinementofthemetaltookformandquantitiesofthemetal becameavailable,artistsandartisanbegantounderstandcertainbeneficialcharacteristics.Onewas thelowmeltingtemperature,muchlowerthancopperoriron.Oncemelted,ithadgoodfluidityand couldbepouredintosimplermoldsandachievegooddetail.
Zinc-caststatuesdatebacktothemid-tolate-1700sinEurope,whereitwasextensivelypromotedforuseinnorthernEurope.InPrussia,itwasusedonbuildingsandornamentforthenew capitalcityofBerlin.KarlFriedrichSchinkel,thearchitect,artist,andcityplannerpushedforits useinstatuaryandbuildingornamentationintheearly1800s,wherethesilverybluemetalwas usedtoadornthenewPrussiancapital.
InParis,onehastomarvelatthesilveryroofsandornamentationthatdistinguishesthatcity. TheBaronHausmann,PrefectoftheSeineDepartmentofFranceunderNapoleonIII,undertook avastredevelopmentofthefamouscityinthemid-1800s.Thisstartedthecladdingofthefamous mansardsofParis.Supposedly,theBaronHausmannhadarelativeinthezinc-miningbusiness.It couldalsohavebeenthatHausmannwantedtohaveacrèmecoloredstoneusedforthewallsofhis buildingdesignandtheuseofcoppermayhaveledtostaining.Oneofthegreatbenefitsofzincis thatitsoxidesdonotstainadjacentmaterials.
Oneofthemainsourcesofzincwasthemine,LaVielleMontagneinKelmis,called LaCalamine inFrench.Thisarea,ontheborderofGermanywasthesourceformuchofthezincusedFranceat thetimeofthisadornmentandreconstructionofParis.LaVielleMontagnestartedinthe1400sas asourceforzincusedinmanufacturingbrass.TheLaVielleMontagneZinMiningCompanywas formedtosupplyPariswiththezincneededtoredevelopthecityunderHausmann.Thecompany becameVMZincandisoneofthelargestsuppliersofzincintheworld.
ThezincminesaroundVielle-Montagne,hadbeeninusesinceRomantimesandthisreadily availableorewasidealformakingastatementforFrance.Asearlyas1815,someofthefirstroofsof Pariswerebeingcladinthissilverymetal,zinc,andtodaycloseto90%oftheroofsofthegreatcityare stillcoveredinzinc.UNESCO,theUnitedNationsEducation,ScientificandCulturalOrganization isconsideringmakingthezincroofsofParisaWorldHeritage.
ThePrussiansourceofzincwastheareaknownasSilesia.Silesia,aregioninpresent-day Poland,producedzincthatwasknownforitslowsulfur.Veryextensivemanufacturingofzincproductstookplaceinthisregion.ThecentralpartofEuropeminedandproducedmuchofthezincused intheworldduringthe1800s.
Itwassoondiscoveredthatcoatingironinmoltenzincwouldprovidegalvanicprotectiontothe ironandlatersteel.By1830,coatingironwithzincwasinwideusethroughoutEurope.Laterthat century,steelwasinventedandovertookironasabuildingmaterial.Asthelesscorrosionresistant steelcameintomajorusethelaterpartofthecentury,coatingsteelwithmoltenzincasasacrificial layerbecameamajorenterprisethatcontinuestoday.Thevastmajorityofzincusedtodayisto protectsteelbyhotdippinginbathsofmoltenzinc.
