Metallography and Microstructure in Ancient and Historic Metals

7/31/2019 Metallography and Microstructure in Ancient and Historic Metals

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MEALLOGAHYAND

MCRORUCURE

OF

NCEN

AND

ORC MEAL


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MEALLOGHYAND

MCRORUCURE

OF

NCEN

AND

ORC MEAL

DAV SCOTT

H GET CONSERVATON NSTUEHE J PAU GETT MUSEUIN SSOTO T TP OOS


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Ft a bak : Phtmgaph f a Wtz

stl pll fm th Da g fIa Th stl shyput a as, a was ma a ubl

pss Vs appa ak Th palt appas a

ay f ls u t ffs spag Th

wht ls a mtt; th asal lght

paths a h phsphus Ths ubl stl s a

hgh-qualy put f at hst sga

Cl tf tt th sl a x420

ublats Cat Ia Akff GC

Et Ia Ak

Thal Dawg: Jat Spha Equz

Cts: Fgus 73-74 Cutsy f h Ama

Sy f Tstg a Matals; Fgus 106, 45148, 62 t Dll htgaphy Dpatmt,

Isttut f Ahagy, L Fgus 1-812-20

264055198-212 aw by Jat Spha

quz; Fgus 198-212 Cutsy f th ta

tal Cpp Rsah a Dlpmt Assat;

Fgus 75-80 Ds Kly; C, Plats 1-20

Fgus 9-11 21-25, 4154: Da A Stt

Dsg: Maquta Stal Dsg, Ls Agls, CalfaTypgaphy FamMak / Ab Gaam a Gll Sas

tg T Wah ss, Lt

1991 h J aul Gtty ustAll ghts s

Publsh assat wth Ahtyp Bks whh akwg a gat

fm th Cmmss f Eupa Cmmuts

Pt Sgap

Lbay f Cgss CatalgugPublat DataStt, Da A

Mtallgaphy a mstutu f at a hst mtals/

Da A Stt

p m

Ilus bbgaphal fs a x

ISBN 0892361956 (pbk)

1. Mtallgaphy 2 AllysMtalgaphy 3 Mtallgaph

spms 4 At bjtsCsat a stat

I T

TN690S34 1991

669'95dc20 9119484

CP


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H G CONSRVAO N

e Gey Cseva Isue a eag

ga f e . Paul Gey us was ceaed

1 8 addess e cseva eeds f u

culual eage e Isue cducs wld

wde edsclay fessa gas

scec eseac ag, ad dcuea.

s s acclsd ug a cba f

use jecs ad cllabave veuesw e gaas e USA ad abad.Secal acves suc as ed jecs ea

al cfeeces, ad ublcas sege

e le f e Isue


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ALE OF ONTENT

ewd IXPefae XILst f Cl Plates and gues XlliCl Plates e Natue f Metals

e Mstutue f Anent Metas 5

3 wased Mateas 1 1

4 e Mstutue f n Bnes 5

5 Ntes n te Stutue f Cabn Steels 3

6 Matenste n wabn Steels 33

7 e eeng f Matenste 35

8 Stutue and Petes f Cast In 37

Cded Mstutues 43

1 0 Reeted Plaed Lgt Msy 4

1 1 Gan Ses f Anent Metas 5 1

1 Metalgay and Anent Metals 57

1 3 Metallga Salng f Metals 6 1

1 4 Muntng and Peang Seens 63

1 5 Redng Results 6

1 6 Etng and Etng Slutns 6

1 7 Muntng Resns 75

8 Madness estng 77

A Aendx: Cn Mstutual Saes 7

B Aendx: Mstutue f Cded Metals 8 1

C Aendx: Madness Values f Dffeent Allys and Metals 8

D Aendx: Allys Used n Antquty 84E Aendx: es and enques n Anent Metalwkng 85

Aendx: Metallga Studes 86

G Aendx: Pase Dagas 1 1

Glssay 1 3

Bblgay 1 47

ndex 1 5 1


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10/182

OWORD

Ifat abut te stuctue f ateals ad

teclgy f aufactue f acet ad stc bjects ad atfacts ca pvde sgt t

te date place f g ad pbable use

vestgats f stuctue ay as be vey

ptat f dcuetat pesevat stat

egy csevat teatet ay decades

bjects f a vaety f ateals ad datg

f pesty t te peset ave bee scetf

cally studed ay f te by etallgapc

tecques Mst f te esults ae scatteed

tugut te teatal lteatue ae se

tes accessble ad fte t publsed at alequetly te eed as bee expessed

atal ad teatal eetgs t cllect

fati ceta types f bects classes

f ateals e pace ad t ake t avaable

as a database publcat s vlue s a

attept t pvde a easued aut f f

at egadg te tecques f etallga

py as tey appy t acet ad stc etals

It s llustated wt ay exaples f dffeet

types f cstuctue daw f avd Sctts

ay yeas fexpeece ts eld f studye pe tat te peset vlue develped

wt te gudace f ak eusse Assc

ate ect gas GC wl be a usefu

bk f studets csevats csevat sc

etsts ad wkes te aea f etalgapy

especally tse seekg t udestad te atue

f cstuctue as t apples t acet ate

als e bk s te st a sees f efeece

wks tat te Getty Csevat sttute s

publsg ateas used csevat ad

teclgy e Getty Csevat sttute

ad te ] aul Getty Museu ave bee

vlved cllabatvely wt ts wk ad

peset ts vlue as cpublses

Miguel Angel Corzo

Director

The Get Conservation Institute

Marina del Rey Calia


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PREFACE

Ts bk bega as a seres f labrary es

ad e aur pes a e prcess f rewrg ad egrag e rgal ex as bee re-

dered re accessble. Tere are ay sudes f

ace ad src ealwrk publsed e

leraure bu s re dcul d a geeral

accu f eallgrapc ecques ad a

erprea fcrsrucure wre prarly

fr e csera sce s ad cserar.

Ts bk aeps ll s gap by pvdg a

gude e srucure f eas r e ae

ras scece perspecve s als useful explre

e ways wc ays ave bee used ace ealwrk.

Tere are ay reass fr sudyg e

srucure f eals. Te prper csera f

bjecs requres r sees eables e cser

var bserve crsrucure. Ivesgave

sudes ay be ecessary rder assess e

degree f crrs r ebrlee f a bjec

A ew cserva reae ay ave pca

s fr e presea f eallgrapc s ruc

ure Cyr Saley S saes a e erarcy

f srucure ca be exaed a ay dffere

levels faggrega ad a e crpra f

eprcal experece f aerals a ere

ca fraewrk as eabed aerals scece

apprecae e effecs f srucure prperes

ad eve e arsc quales f aerals I s

ceraly rue a ealgrapc srucures

eselves are fe vsually cpellg b a

scec ad a arsc sese Meals are eres-

g aerals sce er prperes ca be ap

ulaed ay ways. By cbg eals, by

eag ad quecg by akg e lqud

ad casg e r by wrkg e sape

w a aer r a lae, ey allw a plascy

f vee wle beg saped ad a aly f

fr we a prcess s cpleed

Te srucure f e bk suld ave a wrd

f explaa ere. Te apprac a as bee

ake s descrbe brey wa eals are ad

dscuss pase dagras ad e kds fsrucures

be fud dffere ad releva allys befre

prceedg deal w e praccal applca

f s kwledge: e saplg ad prepara

f saples fr eallgrapc sudy. Te qua-

ave erprea f aly pase dagras as bee cluded ere ad geeral ae

aca ce as bee kep a u.

Te praccal fra e ex als cludes

deals ecg slus ad sr accus f

crardess ad e gra se f eals. Tere

s a legy appedx ) wc exaples f

dffere ypes f allys ad crsrucures are

gve draw fr sudes carred u by e

aur Ts appedx s cpreesve, bu

s ped a e reader wll d eresg

ad frave.Te aalycal daa a ave bee preseed

e bk are qued wu a dscuss f

w e resuls ave bee baed Tere are

ay accus f aalycal eds ad ec

ques suc as elecr crprbe aalyss,

ac absrp specrpey, duc

vely cuped plasa ass specrery ad xray urescece aalyss, ad e r re f

ese ecques are e prcpal eds by

wc e resuls qued e ex ave bee

baed I was e a f e prese ex eer dea l ccerg e cecal aalyss

f eals. Slarly alug crrs ad cr

rs prducs are fe esseal cpes f

ace eals, ere s dealed dscuss f

e aure f crrs prducs gve sce

d s w uld add subs aaly e leg f e

bk Te sel g casg ad wrkg f e

als s as cvered deal by e ex

alug e glssary des prvde se fra

ad c ers used descrbg eals

ad ealwrkg prcesses

AcknowledgmentsTe aur s very graeful e saff f e

Gey Cseva Isue Publcas

Depare fr seeg e auscrp rug

fr edg prg parcular Ira

Averkeff fr er ugul ad dedcaed ed

ral wrk. Jae Erque was respsble fr

redrawg e rgal gures Des Keeley

k e pgraps Caper 1 , ad Mar

qua Saeld dreced e verall desg Na


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ly, Fak esse, Asscate ect

gas, ad a Aeke, lcatsCdat, st e taked te ets

as ad st

e at s als gate t Se Scls

ess asss tace wt te cat te

st es te text

Seeal te tcgas take y te

at wd t ae ee ssle wtt te

e ad assstace ded y tse w ae

geesy deted sales te t te case

atcla I wd lke t tak Nge See

ey, e ead te eatet Cseat ad Mateals Scece, Ist tte Acae

gy, d, cety Sey Csea

t, Natal st, d aes Back,

Iteatal Acadec ects, d;

Rdey Cg, ely Reseac Asscate,

eatet Cseat ad Mateals Sc

ece, d, ad e stdets te

eatet, Nl Se, eate Bs, B

ae, aagkaa Ratak, Nayl

Gad, Adlasl Vatadst

agg, ad ae te I wld lke t ge

taks t te lwg ees te sta at

te sttte Acaegy awck Bay,

Reade St Aeca esty ete

e, ead te tgay eatet; ad

Stat adlaw, Se tgac ecca

At te Gety Cseat sttte I wd

lke t tak, addt, y secetay Rt

Feda, w as caed t ay etyg ad

eattg s cect wt te eaa

t te asct; Nee Agew,

ect Seca ects ad Mcael Scl

g, Asscate Scetst F te a Getty

Mse a st gate t ey day,

ead te eatet Attes Cse

at ad da Stass, Asscate Cseat,

eatet ecate Ats ad Sclte

Cseat

D. DavdA. So

Hea Mueum SeveThe Ge Conevaon Inue


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Plae I. Secio fom a Lisa

dagge hadle.Plae 2. agme of cooso cs

fom a Chese cas o lio.

Plae 3. Seco fom a odoo

boe scle

Pae 4. agme of a bass

medalio fom he La Peose

shweck off he coas of Asaia.

Pae 5. Roma mio fom

Caeby.

Pae . Cooded seco of a

Roma icese be.

Plae . Cas io fagme fom9hcey scaes.

Plae 8. Seco fom a highi

boe vesse fom hailad.

Plae 9. Secio fom a Geek Hem

of abo 120 Plae 0. aa o Age dagge

hi.

Plae I Seco of a slamic

kwe.

Plae 2. Seco of a cooded cas

o caoba fom he owe of

Lodo.

Plae 3. Seco of a cas o

caobal om Sada Case.

Plae 4 Secio of a hghi boe

mio fom Java

Plae 15. Seco fom a sma dia

Woo igo.

Plae . Seco fom a Jaaese

swod blade.

Pae . Lae Boe Age swod

fom Paesie.

Pae 8. Poished ad eched seco

of a lae medieva dia ic coi.

Pae 19 Secio of a sma Lisaceemoia axe fom a.

Pae 20 Secio fom iside hebase of a Geek Hem.

ig. !. Coseacked hexagoal i

cel sce.

ig. 2. aceceeed cbc i ce.

ig. 3. Bodyceeed cbic cel.

ig. 4. Gah of eaosh

bewee sess ad sa.

ig. 5a b. Sess ad sa elaio

fo CC,BCCad CP H; sess ad

sai fo iesiia maeias.ig. . A edge disocaio.

OLOR PE AND GURE

ig . Pogessive moveme of a

edge dslocaioig 8. Dede ams

ig. 9. Poished ad eched view

of a secio hogh a "Daiesye

ecoa fom Ace Coombia.

ig. 0. Poished seco of a sma

cas fog fom he aoa aea of

Coomba.

ig. a-f. Some micosca

feaes i soid soio CC

meas.

g. 2. Relaioshi bewee sige

hase sces CC meas.

ig. 3. Secio hogh coe aoy

axe fom a showig wied

gas.

ig 14. wied gas of god

coe aloy shee.

ig. 5. wi aes i dia ic

cog. . wi aes ic

g. . wi aes i ic

g. 8. Phase diagam fo he gold

sive sysem.

ig. 9. Eecc dagam of sive

coe aloy.

ig. 20 Eecicye

micosces.

ig. 2 Dediic 0% Ag 40%C cas aloy

ig. 22. 0% Ag 40% C eched i

oassim dichomae.

g. 23. 0% Ag 40% C cas aoy

isaig eecic .

g. 24. Woo see igo fom da

gs. 25a,b ad micosces.

ig. 2 Eecc ad .ig 2. Eecc ad dediesg. 28. bos sce woked

wohase aloy.

ig. 29. ad eecoid.g. 30. ocabo hase diagam.

g 3a-d. Beakdow of gas.ig. 32. Cemeie ad eaie.

ig. 33. Coei hase diagam.

ig. 34. a eiecic.ig. 35. hase gais.ig. 3. Coeic hase diagam

ig. 3. gas coec.ig. 38. Discoios eciiaio

i AgC

ig. 39 CA hase diagam.g. 40 CPb hase diagam

g. 4 Cas oggle fom a.

ig. 42. Chiese casboe icese

be.

ig 43. A smal mio of bea

eched boe fom Smaa.

ig 44 Highi boe mio

fom Java

ig. 45 Cas highi eaded boe

of 22% i,% leadad 2%

coe.

ig. 4. Laboaoy eched aoy

of 24% i,% coe

igs. 4-50 Jaaese swod blade

fagme.

ig 5 Paay Widmase

see.

ig 52. Gai boday sce

wh sbga feaes.

ig. 53. Gai sie of kife edge.

ig. 54. Baded sce of a

eched swod blade.

ig. 55. Pa of he eeC hase

diagam.

ig. 5. See il fom id of a

Woo ccible, Decca aea of

dia.

ig 5 Medieval kfe bade fom

Adigey,Sssex Eglad.

ig 58. Phoomicogah of kis

fom dia

igs. 59,0 ech cseel bead.

ig Pa of he eeC hase

diagam fo cas io

ig. 2a- ake gahie i cas

o.

ig. 3. 8hcey cas io scaes.ig 4 Cas io caobal fom

he owe of Lodo

ig. 5. yica vaaios i he

esevaio of sface deai i

ace mealc afacs.

ig . Moed ad oished

secio hogh a boe od

fagme

g. Dawg of he coss secio

of a boe od fagme

g 8a-d. Exames of cooso of

godcoe aloys.igs. 9,0. Lisa ceemoa

axe.

g. . Secio of a coodedfagme fom a Ecadoia gided

coe ceemoal axe.

g. 2. Nomogah fo gai sie

ig. 3. yica sadad fo

esimaig he aseiic) ga sie

of see.

g. 4. yica sadad fo

esimaig he aseiic) gai sie

of aealed ofeos maeias

sch as bass, boe,ad icke

sive

ig. 5. Moig sma secimes

ig. Gidig moed samles.

ig. . Poishig moed sames.

ig 8. Samle soage.

ig. 9. Examiao by oaied

igh micoscoy.

ig. 80. Use of iveed sage

meagica micoscoe.

ig. 8. Dawig of a axe showig

ideal ocaio of same cigs.

ig. 82. wo sames of moed

wie o od.

ig. 83a-c. Holdig sma sames

ig. 84a-d. Embeddig smal

samles

g. 85. Shaes of feie i ow

cabo sees

ig. 8. Commo desciive

micosca ems

gs 8-89. Base sivecoe aloy

coi fom wese dia.

igs. 90-93 slamic iad kwe

cas i a coeicead aoy.

igs 94-9. Cas boe aowhead

fom Paesie.

igs. 9-99. Paesie boe swod.ig. 100. Roma wogh io.

igs. 0-03. Coombia god

coe aloy shee.

igs. 0405. Ecadoia coe

aloy ose oame.

igs. 0-108. Cas aseica coe

axe fom Ecado.

igs. 09 10. Chese boe

icese be.

ig. . ha boe cas bel.

igs 213 Lisa dagge

hadleigs. 4 5 agme of a ha


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bronze containe

Figs16,17. Columbian cas Siear ornamen.

Figs I-120. Cas on cannonba

fom Sandal Castle

Figs 21,22 Bronze Age copper

ngo from Hampshe Engand

Figs 23-25. Roman brass con

Fgs 12627. Tha bonze

conainer fragmen.

Fgs 128-30 God neckace beadrom Colombia.

Figs 31-133 Gold alloy nai and

god ear spool.Figs. 34,135. Tang and blade

secon.

Figs 1363. ron knfe.

Fg 38 Roman coppe aoy coin

Figs 13940. Roman iron na.

Figs. 41-44 Naive coppe fom

he Great Lakes region in North

Ameica

Fgs 45-4. Head of a oggle pn

rom ran

Fgs. 1485. Javanese ron bade.

Fgs. 52 53 Bronze ae fagment

from ran

Figs. 54,55. Laboraory cast

60:40 bass.

Figs 156-59 Glded siver earng

from Jordan

Figs 60 161. Fragmen of a brass

medallon rom Asralian

shipwreck

Fgs 162-164 Fragmen of a smal

Si ear ornamen

Fig 65 Roman mror ragment.

Fig 66. Roman bonze grine

Fig 167. Roman bonzemcrostrucre

Fig 68 Renaissance silver basin

from Genoa

Fig 69. Part o soder bob rom a

repar o he ote adial pane o the

Renaissance siver basin

Fig 170. Section hough he

Renassance siver basin

Fig. 1 Overal vew of a coe

diled pug from he silver basn

Fg 72 Par of he siver shee

etched n acidied poassimdichromae

Fig 3. Section o a circlar

braceet rom Thaand.Fg 14. Strctre o he ccuar

bracee fom Thaiand afer etchng

in alcoholic errc chode

Fig. 5 High magnicaon of

cicuar baceet om Thaiand

showing redeposied copper, copper

sulde ncsions and bonze metal.

Fig. 6 Secon throgh a Roman

bronze bowlghy eched n

acoholc eic choride.

Fig. Early medeva bass sheet

eched n alcohoic ferric chlorideand potassim dchromate.

Fg 7. Recystalzed and heavily

worked gan strucue of brass sud.

Fg 19. Microsrcture o

RomanoGreek ron arowhead

Fig 180 Unusual corosion paten

throgh Byzantine bronze bade

Fig I Heavly eched view of

Byzantne leafshaped bade

Fig 182. Coroded iron knie bade

rom medieval Brain

Fg 83. on knfe bade showing a

weld where diferen peces o ron

have been joned togeher

Fig. 84. owcarbon seel area of

medieval ron knie bade

Fig. I5. Section o panpipes eched

in cyande/persfae

Fig. 6 Fragmen of Byzantne iron

dagge blade showing par of he

edge

Fg 8. Ovea vew o he Roman

coin o Victor en us etched in

acohoic feic choide

Fg 8 Gan sucue of heRoman con of Vcoren us.

Fg I9. Mcrosrctre of grey cas

ron of he eary 20th cenuy.

Fg 190 Grey cas ion showing

graphite lakes and pearlitic nl

Fig. 9 Gey cas iron showing the

cast srcre of the ironcarbon

aoy

Fig. 92. Graphie akes n a ferrite

maix with an nl o pearle

conaning some steadie paches.

Fig 93. Whie cas on showingong cementie lahs an sma

gobar regon of peaite

Fig 194 Whe cast iron etched inMakam's reagen and picral

Figs 19596. Tin ngot rom

Cornwal.

Fig. 9 Tensile poperties impac

vaue,and hardness o wrought

coppen aloys.

Fig. 98. Coppen system.

Fig. 99. Pa of he copperin

dagam under dferen condiions

Fg 200. Coppearsenc system

Fg 20 Copperead binary sysemFig 202 Copperiron bnary system.

Fg 203 Coppergold binaysystem

Fig. 204 Copperantmony bnaysysem.

Fg 205. Copperslver binary

system

Fg. 206. Coppenicke bnay

system

Fg. 207 Copperznc binary sysem

Fg 208. roncarbon system.

Fg 209 a. Leadin system(pewers) b Godsver sysem

Fg 210 Coppersivegod ternay

liqidus

Fig 2 Coppersivegod ternay

soids

Fig 22 Coppenead ernay

sysem.


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1 HE AUR OF MEAL

igre I Cloe-ed hegoui t ell truure Ato g

for of

igure

e-etered uit A

CC ruure h four to erui ell d to igftor of i ot eleetryl

gure 3 Bodyetered ubi uiel A BCC etl two oer u ell d toi igfor of i eleetl rytlBCC etl re boh dutil e dtrog eg ro hroi u ugte d oybdeu

Metas ae a aggegat f ats tat aat

f ecuy ae sld at teeatueese ats ae eld tgete y etallc

ds tat esut f sag avalale elec

ts A egatve elect d evades te

stuctue ad eat ad electcty ca e c

ducted tug te etal y te fee veet

f elects e egatve elect d su

uds te stve s tat ake u te cystal

stuctue f te eta ee ae tee c

tyes f lattce stuctue tat etals eg t

clseacked exagal faceceteed cuc ad

dyceteed cuc

Cos-Packd Hxagona (CPH)Mdels f cystal stuctues ca e ade u f

sees stacked clseacked layes w

aageets ae ssle e eg exaga

ad te te cuc asc stuctue te

clseacked exagal syste te sees eeat

te sae s t evey secd aye ABABAB

g

FacCntrd Cubic (FCC)Layes ca e ult u s tat te td aye f

sees des t ccuy te sae st as te

sees te st w te stuctue eeats evey

td aye ABCABCABC ) CC etals ted

t e ductle

e ca e ecacaly defed

daw ut t we aeed t seet)

Exales ae lead auu ce slve

gd ad ckel g

BodyCntrd Cubic (BCC)Ate c tye fud ay etals tedyceteed cuc stuctue s less csely

acked ta te CC CP stuctues ad as

ats at te ces ad e at at te cete

f te cue Te ats at te ces ae saed

wt eac adg cue g 3

te etas tat atuty ave

etey dffeet lattce stuctues f exale

asec aty ad sut ae e

da ad day t s dyceteed tetagal

Metals ae cystalle slds ude alcdts fwkg ad etg weve f a

etal s cled vey adly as slat cg

te a cystae stuctue ca e suessed I slat clg etal dets ae

cled vey uckly etwee clled eta lates

ad te stuctue tat deves s sla t

glassa ad aageet f ats ate

ta a cystale aay I te usua cystalle

state etal wll csst f a ue f dscete

gas e eta s te efeed t as eg y

cystale A tat ety f etals s

tat tey udeg astc defat we

stetced aeed s s lustated y a

stesssta daga usg ugs MduusM)

YM=strss

tran

la appl

crsssctnal ara

chang n lngth

rgnal lnh

lowrbo ee

oer

tr

igure eltio bewee re d ri

Befe lastc defat ccus ateas

def y te elast c veet f ats tatld te stuctue tgete s eastc defa

t ccus etas ad te ateas suc

as gass wc ave aty t def at

teeatue Glass wl stetc y elastc defa

t ad te eak Metals ca de ast

cally ecause aes f ats ca sl as t eac

te t duce veet s kd f ve

et cat take ace a glassy stuctue

e etals suc as ue ce ae

stetced tey wl eak actue ut ly

afte a ceta aut f lastc defat asccued see gs , a )


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he Natu oMta

2

Figue a, ght Stess a stainelationshi p fo FCC BCC, anCP etals copae with gass

a a typical polye An i ceasein iteato c spacgs isesposib le fo eastic behavo,whil e pastc oveet esutsfo i socatios gvig ise to sl ipWhen this plastic oveent cao longe occu factue wi ll taeplace

igue b, below Stess a stanfo ntestitia ateas Itestitiaeleets ae sall i n size, such ascabo, a ca be isete itothe lattice spacing of soe eta lssuch as steel whch is a itesttialaloy of ion a cabo Itestitials ten to es ie at the base ofs ocatios a ancho theWhen sli p occus cabon is leftbehin an the slocation is heluntil soe highe stess is eacheWhen the stess facto i s eachea eoous ube of isocatons occu that ca ow ove at alowe stess tha oiginall yeuiehence the two yiel

points

Hadne Dlocaton

e adness f a eta is easued by its esis-tance indentatin e etal is indented unde

a knwn lad using a sall steel ball as in te

Binel test) a squaebased diand yaid

as in te Vickes test). In te Vickes test te

esult is given as te Diand Pyaid Nube

DPN )

It is ae f cystals t ave a efect atic stuctue tee ae usually iefectins esent. In

etals edge dislcatins and scew dislcatins

ae te st itant faults see igs 6, 7)

ese cystal faults enable defatin t take

lace at lwe alied stess by sli tan wuld be

ssible if te lattice stuctue was efect. en

VQ

factue poits

typcal bittle ateial (eg, glass)

BCC (eg Fe)

CP (eg Zn) typica aophous polye (eg polystyee)

!FCC (eg, Cu)

stain E

plastic deformaton ICC BCCefoaton Factue

uppe yiel poi nt

Cu substitutioally alloye eg CuSn

Cu una loye

stain

ntestital alloyeg, eC


24/182

Fige his ige shows an extaplae o atos isete i theoignal lattice The plae o theege islocation a its iecton ooveet ae pepeni cul a to thesip plae

gue 7 Pogessive oveet oan ege i slocatio showig slip

a etal s defed te sl takes lace utl a

tagle f dslcats bulds u wc evetsay fute wkg .e. dslcat etage

et As etal s wked, sl laes bece

tcke ad ble . f te etal s wked fu-

te, t ust be aealed eated u t bg

abut ecystallat. Befe aealg te

etal ca be sad t be wkadeed. k-

adeg s acclsed by f exale a

eg at teeatue s ceases te

etal adess value but deceases ductlty

ege islocatiocystal attice

ege islocation

h Nau oM

Notes

e atc ackg fact s a easue f tesace actually used by te ats te lattce. ad FCC lattces ae bt 0 wle te

B etals ave a lwe fact f 0 68 A -

ete l f te lattce wuld be 1 00

2 Ductlty s e used te sese f tesleveet .e . stetcg ad alleablty s

used f ablty t be wked e , aeg.

cystal lattice aer sli p

oveet though cystal


25/182


26/182

tetiay

seoay a

iay a

igue Deite as

2 HE MCRORUCURE OF NCEN MEAL

There are two bac mean of manipulating met

a they can be cat or worked. All the varioumethod by whch cating and workng are car

ried out cannot be examned here n detal, but

the different type o f tructure are decribed.

Castnghere are eentially three type of mcrotructure

that can are during the catng and cooling of a

melt in a mold reardle of the exact nature of

the technology nvolved. Mo t ancent metal are

mpure or are delberate alloy of two or more

metal uch a copper and tn (bronze) or copperand zinc (bra) . The fact that they are impure

an mportant one for the knd of crytal growth

that can occur o a large extent dependent on

the purity of the metal Th i one reaon why the

great maorty of ancent cating how a den

drtic tructure endrte look lke tny fernlike

growth cattered at random throughout the

metal They grow larger until they meet each

other Sometme outlne of grain form between

them, and the rate at whch the meta i cooled

nuence their ie Uually a microcope mut

be employed to make dendrite vble, but on

obect that have cooled lowly, the dendrte

have alo formed lowy and may be vble to the

naked eye or under a binocular bench mcrocope

at low magncaton (x or x0 ) he fater the

rate of cooling, the maller the dendrte. t po

ible to meaure the pacing between dendrte

arm f they are well formed and to compare the

pacing obtained from thoe from known alloy

cat n dfferent mold or under di fferent cond

ton. Arm of dendrite are uually referred to a

prmary econdary or tertiary Fig. 8) .

t may be of interet to record dendrtic arm

pacing for comparatve purpoe even if condi

ton are not preciely known or there a lack of

background nformation n the metallurgcal lt

erature. endrite may be rather fuzzy or

rounded n outl ne or qu te harp and well

dened, dependng on the nature of the alloy and

the cooling condton of the melt. endritc

growth actually one form of egregaton thatcan occur durng catng t i a egregaton

phenomenon that often are n mpure metal or

alloy becaue one of the conttuent uually haa lower melting point than the other. For exam

ple conider the cooling of an aloy of copper and

tn. Copper melt at 1 083 C and tin at 3 C.

When the alloy cool and begn to olid by

dendr tic egregation the rt part of the dendrte

arm to form are rcher n copper nce th con

tituent olde rt , whle the outer part of the

arm are rcher in tin. The reult i that there a

compo tonal gradient from the nner regon of a

dendrtc arm to the outer urface. Such dendrte

are uualy referred to a cored Corng i a common feature in catng of brone arenca cop

per debaed lver etc. t i uualy neceary to

etch a polhed ecton of the metal to nvetigate

whether corng preent or not. ependng on

the amount and nature of the alloyng conttuent

preent, the remanng uid n the nterdendrtic

channel or pace wll then olid to form a df

ferent phae of the partcular alloy ytem. A

phae any homogeneou tate of a ubtance

that ha a denite compoit ion. n practce th

denton mut be interpreted a lttle ooelybecaue very often ancent metallc ytem are

not fully in equilibum condition which mean

that the proporton and even the compoton of

the indvdual phae that are preent n an alloy

may not match the prece vaue that can be

determned from a phae diagram. The ubect of

phae and phae diagram wll be taken up later

n th ecton endrte, then, dominate the

world of ancient cating ee Fg. 1 0) but

there are occaion when other type of egrega

ton occur n addtion to dendrt c egregaton or

when coong condton gve re to completely

different tructure

he other prncpal type of egregation are

normal egregaton and nvere egregaton Nor

mal egregaton occur when the lower melting

pont contituent i concentrated toward the

inner par of the mold, while nvere egrega

tion often aocated wth alloy of copper con

taning arenic antimony or tncan puh the

alloyng element to the exteror of the urface of

the mold . nvere egregaton may be reponble


27/182

h Micotucu oAncint Ma

Figue 9 ight Po lishe a

uetche sectio though aDaie -style pectoal foaciet Colobia Magificato

6

( 60) shows selective coosioof the ete as Note thevey oue ipessio of theeitic shapes The aloy is a1 8% gol % silve 68% coppealloy cast by the ostwa pocess

ige 1 0 a ight Polshesectio of a sall cast og fo theaioa aea of Colobia showig

ieet eitic stucte Heehe agiicatio i s 80 a thesecto has bee etche withpotassiu cyaie/aoiu pesu lfate etchat

for some of the slvery coatgs occasoally

reported the lterature such as the atmoycoatgs o some cast Egypta copper obects

(k ad Kopp 1 933) . Copper lead or gold

castgs ca occasoally be relatvely free of

mpurtes ad o slow coolg o dedrtes may

be vsble. Uder these crcumstaces the metal

may cool ad produce a equaxal, hexagoal

gra structure. A equaxed hexagoal crystal

structure, whch all the gras are roughly the

same sze, radomly oreted ad roughly hexag

oal secto correspods to a deal model of

a metallc gra or crystal. t s the arragemet ofseparate growg crystals that meet as they grow

that gves the hexagoal ature to the deal struc

ture sce ths results the least eergy requre

met. t s a equlbr um structure for ths

reaso, whch the dedrtc structure s ot (see

g. 1 1 ). Oe result of ths s that t may be pos

sble to obta a equaxed hexagoal gra

structure by extesve aealg of the orgal

dedrtc structure. O the other had a de

drtc structure caot be obtaed by aealg

a equed gra structure. Cast metals that doot show a dedrtc structure ca be qute df

cult to etch ad t may be dcult to develop ay

structure apart from the vsble clusos ad ay

porosty the metal. Cast metals ofte dsplay

characterstc sphercal holes or porosty whch

ca be due to dssolved gases the melt or to

terdedrtc holes ad chaels that have ot

bee kept lled wth metal durg soldcato.

the metal cools, the dssolved gases exsolve,creatg reactos wth the metal tself to form

oxdes (for example the producto of cuprousoxde [Cu the copper eutectc acet

castgs) or causg gas porosty the mtal. The

thrd type of structure whch s partcularly assocated wth chll castgs s columar growth.

Chll castgs are formed whe metal cools

quckly o beg poured to a mold. ths type

of structure log arrow crystals form by selec

tve growth alog a oretato toward the ce

ter of the mold. They may meet each other ad

thus completely ll the mold. t s rare to d ths

type of structure acet metals although some

gots may show columar growth.

WogWorkg refers to a method or combato of

methods for chagg the shape of a metal or a

alloy by techques such as hammerg turg

rasg drawg, etc. A l st of useful terms s gve

Appedx E. ur ther detals ca be fod

may of the texts metoed the bblography,

especally those by U tracht ( 1 95 ) ad Maryo

( 1 9 7 1

The tal gra structure of a homogeeous

alloy ca be cosdered as equaxed hexagoal

gras. Whe these gras are deformed by hammerg they become atteed (ther shape s

altered by slp d slocato movemet ad the

geerato of dslocatos as a resul t of workg)

utl they are too brttle to work ay further. At

ths pot the gras are sad to be fully work

hardeed. f further shapg or hammerg of the

metal s requred the the metal must be aealed

order to restore ductlty ad malleablty. ur

ther deformato of the metal by hammerg may

the lead to workhardeg aga ad f further

shapg s requred the aother aealg operato ca be carred out. May obects have to be


28/182

igure I I Soe irotruturleture in oid oution CCetl Cored grin with renntdendriti trutureb Codwored ored grin ul ly nneed hoogeneouhegonl equied grin

d Coldwored nneled elwith ttened grn e Anneed ter old-woringhowing twinned grin Coldwored ter nnenghowing ditorted twn lne ndtrin line i n the grn

shaped by cycles of workng and annealng n

order to acheve sufcent deformaton of thestartng materal whch may be a cast blank or

ngot of metal that must b e cut or shaped nto

ndvdual artfacts. ypcaly annealng temper

atures would be n the range of 00800 C for

copperbased alloys ron and steel. f the metal s

an alloy then strctly the type of anneal ng oper

aton should be speced process anneal stress

relef annea sold soluton anneal etc. me s an

mportant factor as well too lengthy an anneal

may lead to gran growth and a weakenng o f the

structure of the artfact; too short an anneal andheterogenety and resdua stresses may not be

emnated sucently here are other practcal

problems assocated wth annealng dependng on

the metal concerned; for exampe when debased

slver alloys usually slvercopper alloys) are

annealed by heatng n ar they are able to

undergo nterna oxdaton. A black skn of cuprc

oxde forms CuO) overlyng a subscale of

cuprous oxd e Cu) whle oxygen can dffuse

nto the alloy attackng the readly oxdzed cop

perrch phase and producng nternal cuprteembedded n a sverrch matrx for further

detals see Charles and Leake 1 97; Smth 1 97 1

Th Mioutu oAnint Ma

7

Schweer and Meyers 1 978 ).

Coldworkng and annealng ca n be combned nto one operaton by hotworkng he

obect to be worked s heated to near red heat and

then mmedately hammered out. he two pro

cesses namely coldworkng followed by anneal

ng and hotworkng wll gve essentally the

same mcrostructure of worked and recrystalzed

grans so t s always not possble to know f cold

workng and anneang has been used n a partc

ular case although there may be other ndcatons

that have a bearng on the nterpretaton o f the

resultng structure see gs. 1 1af 1 ) Somemetals such as ron usually must be worked nto

shape whe they are red hot he forgng of

wrought ron whch contans slag globules as

mpurtes produces a worked structure n whch

the slag gradually becomes elongated or strung

out nto slag strngers along the length o f the

obect. t s mportant to note that most nclusons

n ancent metals do not recrystale as a result of

hot workng or workng and anneang they

ether are broken up nto smaler partcles or they

are lattened out as the workng process proceedsacecentered cubc metals except for

aumnum recystallze by a twnnng process


29/182

he Mirostrutur oAncent Meta

Figure Reltionhi etweeningle he tuture in CCetl ued in ntiqity.

8

orig inl t teril howng

dendriti egregtion

etenive nnel ing wil lreove the egregted ndored trtre

oldwored ditorteddendrite

deored grin with oe trnine evident on hevy woring

equ i-ed hegonl grin

wored deored gr in nowhowing ent twin nd trinline

hot-woing

nneling nneling

1

reytlli ed nd twinned grinwith tright twin li negrin ize uuly ller.

New rtal that grow followng the annealng of

oldworked faeentered ub metal uh a

gold opper lver and ther allo produe the

effet of a mrror reeton plane wthn the r

tal wth the reult that paralel traght lne an

be een n ethed eton traverng part or all of

the ndvdual gran ofthe metal (Fg 1 ) After

annealng the twn lne n the rtal are per

rerytlli zed nd twinned grinwth trin li ne ent nd trighttwin line withi n grin

fetl traght the ma not run omplete

through ever gran but the are traght. f the

gran are ubequent deformed then the twn

lne wl alo be deformed n polhed and

ethed pemen the appear a ghtl urved

lne n heavl worked metal lp of rtal

plane an our n ndvdua rtal reultng n

a ere of parallel movement that an be een n


30/182

etche ecton a a ere of ne lne n ome of

the gran. hee lne are cale lp ban ortran lne Another feature that may how that

metal ha been healy worke the preence of

a brou morphoogy n the mcrotructure h

may occur when gran hae been lattene out by

hammerng proucng an elongate tructure

commonly ecr be a a "texture effect . When

th metal anneale to prouce a recrytalle

gran tructure the recrytallze materal may

tl how a preferre orentaton or a brou

nature h an extreme example of the fact that

recrytallze gran are not foun to be completely ranomly orente. epenng on the

amount o f colworkng that the metal ha

recee t wll be able to recytalze at ucce

ely lower temperature whch are markely

fferent for partcular metal. For exampe

healy worke pure copper capable of recry

tallzng at 10 ron at 560 C znc at 10

tn at 1 an lea at 1 C

h why metal lke pure lea can be bent

back an forth at room temperature wthout

workharenng they are effectely beng hotworke at room temperature. Aloyng eement

an mpurte wl of coure affect recrytallza-

ton temperature a wll gran e an the egree

iu 1 3 hoomi oah o a sion houh ao alloy a om an showin wnn ainsa hin wih i hloi soluion (ao300). o ha h oosiy in h mal has no bnlm ina by woin

h Miuu An in Ma

9

of coworkng

he percentage of eformaton or egree ofcolwork uually expree n term of reuc

ton of heght of the pecmen h.

hinitial

oldwork

hworked

h . ta

100

t often cult to remoe the egregaton

that occur urng the catng operaton an

many ancent obect that were worke to hape

from a cat ngot tl how ome corng or rem-

nant enrtc tructure een though the obectwa ubequently worke to hape. Varaton n

compoton are not conne by the new worke

gran tructure an appear upermpoe upon

the gran when the pecmen etche (g. 1 3

1)

he kn of twnnng occurrng n CP met

al hown by the tructure of the nan nc

con n gure 1 5 Whle lp an twnnng are the

man metho by whch nc crytal accommo

ate platc eformaton there are tuaton n

whch nether of thee eent can occur rectlyh can happen when znc crytal are com

pree parale to the baal plane or where

crytal are retrane from moement uch a n

u 4 Twinn ains o ol-o alloy shom isa ni Colombi a si o Naio.Coosion whih aas y h oulins winains o h ysals wihou hin. Siaons houhh son a u o sliv oosion as a sul osaon n h wo al loy h saion is uo unqual isibuion o o an ol in h

hamm sh Annalin wins a sah shownha annal n was h inal sa in manuau. 20.


31/182

The Micstucture ofAncient Metal

Fgure 1 5, right wn planes i n

Indian zinc coin.

10

Figure

1 6

far right Twin planes n

zinc.

the usual poycrystaline solid Under these con

dtions , stress can be relieved by the movement of

the basa plane axis The axes of the bend ae con

tained in a bend plane which bisects the included

ange of bend and which has no dened crystallo-

graphic indices he bending mechanism

involves slip, since individual basal planes must

move elaive to each other for bending to occu

Although in some cases the volume of metal

involved in a series of bends is sucient to pro

duce macroscopic kinks bending often occurs

around a very large numbe of closely spaced pa

ale axes giving the effect of a curve When suchdeformed structues ae anneaed close to the

melting point , a coalescence of the ne bend seg

ments into coarser units occurs (Figs 1 6 1 7).

basal panes

bend plane

bend pane

rystatWn n ZnC C

_basa pa

Figre 1 7. Twin panes n nc


32/182

3 WO-HAED MATERAL

Fi 8 has iaam o hol-silv sysm No ha bohmals a oly sol bl inah oh

Apart from compo tonal varaton produced by

egregaton o r by ncluon, the varete ofmcrotructure produced by the preence of two

or more phae n metal have not been dcued.

Some reaon why more than one phae can be

preent are dcued n the folowng ecton:

1 Eutectc tructure2 Eutectod tructure3. Pertectc tructure4. Wdmanttten tranformaton5 contnuou precptaton n termetallc compound formaton

Immcble tructureWhen two or more) meta are mxed

together to form an alloy there are a number of

dfferent poblte regardng ther mutual ou

blty Uually a phae dagram (or equlbrum

dagram a t ao known) mployed It

eentally a map that can be ued to predct what

phae hould be preent n the alloy at equb

rum t mportant to tre that dagram uu-

ally only refer to very lowly cooled melt whchrarely occur n archaeologcal materal. h doe

not mean that t uele to conult phae da

gram t mean that the nformaton mut be

1050

000

nterpreted wth cauton and preferably after

experence wth ancent alloy ganed by mcrocopca examnaton.

When two metal are mxed together there are

three man poblte. he rt a old alloy

howng complete od olublty of two metal.

example the range of aloy formed between

lver and gold. Gold oluble n lver and lver

oluble n gold he phae dagram that reult

from th knd of alloy how ut one od phae

preent at all temperature up to the oldu. he

odu lne eparate the regon o f old metal

from the paty tage of oldcaton at temperature above th lne A the temperature re the

alloy pa through a paty emold regon n

whch ome lqud preent n equ brum wth

ome old. h contnue to the lqudu lne

and above th ne the alloy preent a a lqud

met he lqudu ne eparate the paty tage

from the lqud melt above Fg 18

In coolng from the molten tate the alloy

undergoe the folowng tranton:

L L a awhere L lqud and a od.

min ono u ol

950 soli soluion

0% ol1 00% silv

50% ol50% silv

1 00% ol0% silv


33/182

wphaed Mateia

12

Figue 9 Euei he gmof ileoe lloy.

f no corng or other form o f egregaton are

reent then the mcrotructure wl be a collecton of equaxed hexagonal gran of unform

comotonthere wll be only one hae

reent

he econd oblty that a old alloy can

how only artal olubl ty of the metal n each

other. One exame ver and coer. There

are three rnca tye of hae dagram that

can are from th tuaton he mot common

the eutectc tye econd the eutectod and

thrd the ertectod. The thrd oblty

that the two metal are comletely mmcble neach other

Eutectc StuctueSlvercoer alloy are examle of the eutectc

tye and have the folowng charactertc the

olublty o f coer n lver and of lver n co

er fall a the temerature fall (th a general

charactertc for mot aloy) and there one

temerature at whch the lqud melt can a

drectly to old The eutectc ont. At th ar

tcular comoton and temeraturewhch

vare of coure deendng on the nature of the

alloyng conttuentthe lqud melt ae toold whch twohaed and cont of ne

late of alha hae and beta hae nterered

n each other (ee Fg. 13 5a b)

here a large area where aha hae coex

t wth lqud and a mlar regon where beta

hae coext wth lqud (Fg. 1 9) . f an alloy of

comoton B cooled down from the melt

then the folowng tranton wll occur

L t L t + eL ( e +

where t = temerature.

The nal old tructure therefore cont of

(e + . The orgnal alha wll be reent aether gran of alha old oluton or a dendrte

of the rmary alha whch wll robaby be cored.

he nllng around the aha gran wll then con

t of the alha + beta eutectc a a ne nterered mxture and under the mcrocoe n

etched ecton wll loo omethng e Fgure 0a.

euei oi

!lloy C

lloy B

omoiion


34/182

gue 20a b Eutetitye

mitutue.

w-phad aa

infill f alha + beta euteti alha + beta euteti

a

dendite f alhaualy ed

Figue 2 1 middl e left. he feathey natue f dendti in a 60% Ag 40% Cu ally that ha been at. Ethedn taium dh mate x35. Whil e the

dendite

an be een lea ly at thi magn ifiatin the eutetiinfill f + annt be eenigue 23 bttm eft 60% Ag 40% Cu al y il utatngthe natue f the eteti infil in whih the e -h hae ethe da and the ilve-ih hae ethelight Elet n-be analyi f ne f the dendti am that aea hee a da glbue give an analyif 92% Cu 8% Ag ending vey well inmtin t the ft ld fmed fm the met inthe hae diagam f Cu-Ag ethed n alhl eCand taium di hmate x 1 60

gain f aha

b

igue 22 midd le ight The ame ally a gue 2 1 60% Ag 40% Cu ethed i n taium dihmate x I 00he

euteti hae i jut beginn ing t be

elved int a fine ee f line in the etin

Figue 24 bttm ght Wt tee ingt fm I nd iahwing fagment f ementite needle with an infi l feutetid eaite + FeC x300) ethed in nita.Wtz teel ingt fm Ind ia wee high-abn tee(ften ve 08% abn at in uibl e and ued fthe manufatue f wd bade and the qual itydut he eutetid may be im ila t the euteti


35/182

Tw-phased aea

4

igure 25ab a an microstructures A tyical eutecic alloymicrostructure

igure 26 Eutectic a a

he coolng rae deermnes wheher he org

na alpha phase s presen as dendres or as hexagona grans Usually n archaeoogcal maerals

he prmary alpha wl be dendrc and cored;

aer workng and annealng may remove den

drc segregaon and grans ofalpha may become

more apparen s beyond he scope of hs ex

o provde a quanave nerpreaon of he

phase dagram, bu wha can be sad s ha as he

euecc pon s approached here wll be corre

spondngly less nal phases of apha or bea

As he area of alpha s approached here wll

be ess euecc presen and more alpha As healloys approach he bea sde of he dagram he

same varaon s found he alloys are progres

svely rcher n bea and have ess euecc n wo

phase alloys where dendrc segregaon has

occurred he proporon of he w phases wl

no be q e wha shoud be a full equlbrum

he aloy a composon A (g 1 9 wl have

a slghly dfferen composon n erms of he

dsrbuon of he wo phases As cools down

he followng sequence should occur

L ( ( L (he resulng srucure wll hen be alpha

grans wh a hn lm of bea surroundng hem,

or alpha dendres wh a frnge of bea (g 5

a

ala en rtes usa y core

some alha + beta eutecticbecause of nonequil ibriu cooling

eutectic mxwil consstonly of aha

bea

A he euecc composon he qud me

passes drecly o so d and deally wll conss of ane nermxed marx of alpha and bea phase

(g 6.

A feaure of he mcrosrucre of euecc

ype aloys s ha here may be a depeon of par

of he euecc phase near he grans or dendres

or example, suppose he orgnal dendres are

alpha phase wh an nll ofalpha bea eueccSome euecc alpha consuen can mgrae and

on he dendr c alpha whch wll leave a frnge

surroundng he dendres appearng o conan a

more homogeneous zone before euecc nllngs reached (g .

One of he neresng changes ha can occur

when a wophased aloy s worked s ha eher

one or boh phases can become elongaed or

sru ng ou much lke slag srngers n wrough

ron, along he drecon of he workng of he

alloy Slag srngers are he brokenup remnans

of slag nclusons n wrough ron ha become

elongaed upon hammerng he ron o shape n

heory one wold expec he process of workng

and anneang o remove any orgna dendrc

segregaon and o produce worked and recrysal

lzed grans wh a euecc nll , dependng on

he composon of he orgnal raw ngo ow

ever s ofen very dfcul o remove he nal

dendrc srucure and nsead he mcrosruc

alha grains eta flms between grains


36/182

Figre 7 right Etectic aertes i a tyical eutectic alloy

Figue far ight ibrousstrcture i a tyical heaviywore two-hase aloy.

Fige 2 an eutectoi in a tibronze aloy.

eutectic

eutectic elete nalha ear enrites

5

elogate en ritic remats

Twphad aa

etectc hase fil l

core alha en rtes

light ble eutectoi where eltahase has the comosition C Sn

ture tend to onit of elongated ribbon of one

phae with the euteti inbetween The length-

tobreadth ratio of thee elongated tringer then

give ome idea of the extent to whih the alloyha been hammered outvery thin tringer ug

geting more evere deformation during manu

fature Sometime aloy alo have a brou

quality or the ame reaon ig 8)

Common example ofimpe euteti ytem

in anent metal are thoe of debaed ilver arti

fat, whih are uually ilveropper alloy and

oft oder whih are leadtin aloy

Eutectod S tructures

he eutetoid phae i imilar to the euetitruture the prinipal differene being that the

eutetoid reation our when an already exit

ing olid olution tranform into two ditint

phae The type of phae diagram that give rie

to eutetoidtype tranformation are neearily

more omplex beaue there are erie of hange

in the olid a it ool to room temperature There

are two important eutetoid tranformation in

arhaeologia metal: thoe in tin bronze and in

arbon teel for one example ee ig ) The

form the eutetoid take in bronze and teel i

not the ame In bronze the eutetoid ontitu

ent i made up of the two phae, alpha the

opperrih olid olution of tin in opper) and

delta an intermetalli ompound of xed ompoition, CS n) hi eutetoid phae begin

to appear in the mirotruture between about

5% to 1 5% tin and above) depending on the

ooling ondition of the alloy It i a light blue,

hard and brittle material that often ha a agged

appearane he truture i often haped by

grain bounday edge and the blue delta phae

often ontain mall iland of alpha phae di

pered through it ig 9) If there i a lot of thi

eutetoid phae preent, the bronze i difult to

work Proper annealing of bronze with up toabout % tin will reult in a homogeneou olid

olution o f alpha grain that an then be worked

to hape muh more readily beaue the hard and

brittle eutetoid ha been eliminated

Eutetoid in the bronze ytem originate

from a omplex erie of hange that are not

delineated in detail here, but are ummarized a

follow

1 .The alloy passes through the alpha + liquid

region as it cools.


37/182

Tw-phad aras

6

Figue 0 Sgnifcant region of theironcarbon hase agram

t reache a tranton at about 798 C and

a pertectc tranformaton occur

3 A beta ntermedate old oluton eult4 On coolng to about 586 dc the beta phaetranform to gamma

5 At 50 C the gamma old oluton tranform to the nal old mxture of alpha deta eutectod.

Becaue the eutectod n the coppert n y

tem rather dfcult to follow, mot textbook

on the ubect ntroduce the dea of eutectod

tranformaton by lookng at the phae formedwhen carbon added to ron to produce tee,

and the carbon content ncreae cat ron

Mot ancent teel were made from ron con

tanng up to about 1 % carbon, although not

only the carbon content of many ancent art

fact very varable n dfferent part of the ame

obect but many of them ony contan about

0. 10. 5% carbon. Thee lowcarbon tee were

however very mportant product and could be

ued to produce excellent edged tool

The eutectod formed when the autenteold oluton (gamma phae) decompoe at

about 77 C to form the two new old phae,

ferrte and cementte he combnaton of thee

alloy A

Ylaustentite

two conttuent a a ne colecton of mal

plate caled pearlte he name ferrte gvento the pure ron alpha phae gran, whle cement

te (eC) another very hard and brttle contt

uent, a compound of xed proporton beween

ron and carbon

Conder the coolng of an aloy from above

900 C, n the autentc regon of the phae da

gram wth an average content of carbon repre

ented by the lne for aloy A n gure 30 Acoolng proceed autente (gammaphae) gran

wl eparate out and a the temperature fall fer

rte begn to eparate from the autente at thegran boundare o a the temperature fall

the gamma phae become rcher n carbon and

the ferrte loe carbon untl t reache a low of

003% carbon whle the autente reache the

eutectod compoton at 08 % carbonA thetemperature fal below 77 C the autente

decompoe by a eutectod reacton nto ferrte

cementte The change can be repreented a

ymbol

Aoy A

a

at about 80 C)

a a + Fe C) a beLow7C)

austentte cementte

earlite + cementite

o2 % carbon


38/182

Figure 3 1 ad Breakdown of y

grains in the iron-carbon system

y

grains(above 850)

at y gains

y

grains

(abot 800)

or as a series o drawings at dierent temperatures

on the way to room temperature (Fig. 31ad)

The cooling o alloy B, shown on the portion

o the ioncarbon phase diagam (Fig . 30), ol-

lows a line leading through the eutectoid point

with a composition o 0.8% cabon. Fo this par-ticular alloy the microstructure, i cooled slowly,

would consist o an intimate mixture o pearlite

(alpha

+

FeC) . I n the case o the ironcabon

eutectoid, the initial appeaance is very similar to

that o the eutectic mixture drawn peviously

(Fig . 26 ) I the rate o cooling o alloys contain

ing pearlite as a constituent inc reases then the

spacing between eutectoid constituents becomes

progessively fne I the cooling rate is very ast

then the true natue o the phases that might orm

on a phase diagam cannot be shown becausenonequilibrium cooling conditions would be

involved. What happens in steels in ast cooling is

very important, and new phases, such as maten-

site, can orm, which has an extremely hard and

brittle needlelie structure (see Chapters 6 and 7)

he cooling o alloy C ( Fig . 30 ) whose posi-

tion is shown on the phase diagram, produces a

dierent b ut analogous series o tansormations

rom the austenitic egion:

Aloy Y Y Fe3CY Fe3C F3Cj

+

Fe3C

Two-phased Material

17

a grains

(about 727 C)

+ FeC

eutectod

a

(beow 727 C)

he fnal structue will usually consist o cementite

flms or a continuous cementite network between

the pearlite egions (Fig. 32).

pearlite eutectod

Figure 32 Cementite and pearlte.

Peritectic Structures

Peritectic stuctures arise rom a type o transor

mation that may seem ather peculia at st

sight. t is unusual in the sense that a liquid reacts

with an existing solid phase to orm a new solid

phase. An example can be taken rom pat o the

coppertin phase diagram (Fig. 33) to illustrate

the typical shape o the phase system in peritectic

alloys

loy A cools down rom the melt with about

8% tin content. Ignoring o the moment the

complications produced by coring, as alloy A

cools down, initially an alphaphase solid solution

o tin i n copper separates out, while the liquid


39/182

w-phaed aeras

Figre 33 Coer-tin hase

iagra.

8

Figre 3, right a an ertectic

Figure 35, far ight. E hase grains.

20% S

h lef ge pogrevely rcher n n. A rec

on now occur bou 800 C beween h lq

ud nd he lph phe whch produce new

phe be Snce lloy A occur n he lph be regon of he dgrm ll of he nrch lq

ud wll be ued up before he lph phe com

pleey dolved, nd he lloy wll hen con of

ph

be cryl:

Aoy A iquida iquid (inrich)iquid (inrich) a

na srucure a grainsOfen he perecc econ gve re o precp

on of he new be phe boh whn he

lph cy nd lo he grn boundre o

h he lph h rher rounded conour

(g. 3.

An loy of compoon B on he phe d

grm g. 33) r o old by producon ofph phe grn bu hee grn hen rec

wh he remnng lqud bou 800 C nd re

remaing alhahase grains

beta rouce b eritectctransormaton

compleey convered o new grn rucure of

be grn:

Aoy B iquid a iquid (inrich)a + iquid (inrich)na srucure grains

One of he dfcule of he perecc rec

on h rely poble o ge compleeconveron of lph grn no be becue lph

grn become covered wh cong of be

hey rnform nd he lm o fbe hen preven

he dffuon of nrch lqud o he lph grn.

he reul h here very ofen core oflph

grn ef even f he phe dgrm ugge h

ll he mer hould hve been convered o he

econd phe. A complced exmple gven by

he nl rucure reulng from n lloy conn

ng 70% n nd 30% copper S ome of hee

lloy were ued uully wh bou 0% n he lloy specuum whe lloy ued nce

Romn me for he producon of mrror. In

(eta hase coating (CuS neventng eritectic reactio

eutectic ( Sn


40/182

igue 36 Copezinc paseiagam

theory th alloy hould imply be a mixture of

the eutectic (eta and tn) however thee alloyoften how a nonequbrum tructure wth ep

lon phae gran (Cun) coated wth eta ()phae gran (Cun) n a eutectc mixture of

( n g. 35)Many of the mirror ued in Roman time

were ether made ung hightn leaded brone

wi th t n content of 0% and lead variable

(typicay 51 %) o r they were made wth a

more common owtin brone alloy whch wa

then tinned on the urface to produce the dered

coor.There are other unuual feature n the

coppertin ytem (ee Fig 1 98 99) uch a

that hown by the coolng of an alloy with about

1 % tn urng coolng of th alloy gamma ()

phae crytal tart to eparate out at a tempera

ture of about 7 1 5 C. At lghly below 700 C

freeng i compete and al the qud tran

formed to gamma olid phae At about 650 C

the eta () phae tart to form from the gamma

() unt a temperature of 60 C reached At

about 60 C the redual gamma () decompoe

to form multaneouy the lquid eta () phae

C000

00

800

700

1 00% Cu0% n

20% n

wphased aea

9

A olid alloy melt a a reult of coolng durng

thee phae changea rather unque occurrenceAn alloy ytem of nteret n whch a ere of

pertectic tranformaton can occur the

copperinc ytem (bra; ee g 0) . Mot

copperinc alloy of antquity were made by a

cementaton proce that had a an upper lm t a

nc content of about 8 % Znc ore wa mxed

wth copper ore and the two were melted

together drecly o that the nc wa aborbed

nto the copper during reducton thu avodng

o of nc whch bol at 907 C Mot ancient

inc alloy therefore poeed an alpha phae orcored dendrtic tructure. owever metallc nc

wa alo produced; for example an all oy contan

ing 87 % nc wa reputedly found n prehtorc

ruin i n Tranylvana whle in ancent nda and

China metal lc nc wa produced

he brae are generally divded nto three

categore depending on the phae type alpha

brae wth up to about 3 5% nc; alpha betabrae wth between 35% and 6.6 % inc; and

beta brae wth between 66% and 5 0.6 % nc

A nc content ncreae the brt le phaebegin to appear and thu alloy wth more than

iqu i

alloy A alloy B

0% n


41/182

Twphased aera

20

Figre 37 grai i coe- inc

50% znc are generall avoded Beta phae

brae are ver much harder than the alpha andcan wthtand ver lttle coldworkng he beta

phae begn to often at about 0 C (a the lat

tce change from an ordered to a dordered

tate and at about 800 C t become much

eaer to work. The alpha brae whch nclude

mot of the ancent pecmen are much better

when the are coldworked and annealed rather

than hotworked becaue f hotworked mpur

te tend to egregate at the gran boundare and

make the bra ver weak

hee tpe of tructure are eentall mlar to the poblte gven for the ecton of the

coppertn dagram examned bre earler (g .

33 An allo of compoton A wll havng

paed below the lqudu lne begn to precp

tate out alpha gran, whch are then partall

attacked and converted to beta durng oldca

ton o that the reultng tructure cont of

alpha beta gran (Fg . 36 .Wdmansttten Tansfomatons

he copperznc allo ma appl to a bref dcuon of the Wdmanttten tranformaton.

he Wdmanttten tructure reult from the

precptaton of a new old phae wthn the

gran of the extng old phae. t thu qute

dfferent from the martent c tranformat on

whch eentall a nglephaed tructure uu

all occurrng a a nonequlbrum component of

quenched allo. Martente a collecton ofne

nterectng needle that can form n allo cooled

ver quckl. Uuall the allo quenched b

plungng t nto water or ol from a red heat n

contrat, the Wdmanttten precptaton thereult of one old phae at a hgh temperature

decompong nto two old ph ae at a lower

temperature Th precptaton uuall occur at

the gran boundare of the ntal crtal and a

plate or needle wthn the gran themelve,

whch have a partcular orentaton dependng on

the crtallographc tructure of the orgnal cr

tal

n the cae of allo B (g. 36 , a mxture of

about 5 8% copper and % znc we can follow

the precptaton of the alpha old oluton fromthe beta hgh temperature regon

n Fgure 3a the beta gran are hown a

the would appear at about 800 C or f the allo

wa uddenl quenched n water whch would

prevent t from decompong nto the alpha beta regon The appearance of the gran ut a

homogeneou old oluton of beta gran F gure

3b how the nature of the Wdmanttten pre

cptaton upon coolng to room temperature. f

the tructure annealed or heated to about 600

C then t can become qute coare and the alphaphae ma grow nto large crtal wth the back

ground becomng a ne mxture of alpha beta.Wdmanttten tructure alo occur n

ancent teel a a reult of the workng proce o r

delberate heat treatment ued durng manufac

ture. Ver often Wdmanttten precptaton

onl partall carred through the gran o that a

agged effect produced. t ueful to return to

the roncarbon dagram (g 30 at th tage n

order to dene a few common term Steel

origial grai at 800 C origia gain bouarie matrix robably mi x of


42/182

Figue

Discotiuous

recitatio i AgC

contanng l carbon than th amount ndd to

mak th utctod tructur comlt ar calldhypoeuecoid sees whra tho contanng car

bon n xc of th utctod comoton (and

u to 7% carbon) ar uually calld hypereuec

oid sees Th uctod comoton tlf occur

at 08 % carbon n hyoutctod tl thr wll

gnrally b mor frrt than rqurd and th

calld th proeuecoid(or fr) rrie n hyr

utctod tl thr wll gnrally b too much

cmntt to form a comlt utctod and th

calld proeuecoid cemenie

Proutctod frrt occur n vral dffrntha n th lowr carbon tl of antquty t

charactrtcally found a xtnv ara among

cattrd land of arlt h accordng to

Samul ( 1 980 ) hould b calld massedrrie n

tl narng utctod comoton t h frrt

uually found a thck lm locatd at what wr

orgnally th auseniic grains Th calld

grainboun rrie Frrt may alo b found

n th form of broad ndl whch can b c

ton of lat of frrt occurrng a a Wdman

tttn attrn wthn th arlt A dcrtvchm for om of th varou form of frr t ha

bn dvlod by ub (n Samul 1980;

Andx A for nam of frrt ha n low car

bon tl and a gloary of trm)

Dsconnuous PrcpaonAnothr ty of ha araton of mortanc

dcontnuou rctaton A good xaml

affordd by corlvr aloy ud n antqu ty

T C

00% Ag

wphased aea

2

Vry oftn th lvr wa dbad to om xtnt

wth cor artly to mak th alloy hardr andalo to rduc th amount of lvr bad lvr

obct thn oftn cont of lvrrch gran n

whch th cor ha not yt bgun to arat

out a t hould accordng to th ha dagram

Th oluton of cor n th lvr gran

thrfor n a mtatabl tat and can b rc

tatd lowly wth tm at th gran boundar

Prctaton of th natur calld dcontnu

ou whn t occur at th gran bou ndar h

ntal art ofth ha dagram hown blow

(Fg 38)A tycal lghtly dbad lvr alloy hown

by alloy A on th lvrcor ha dagram

Not that t cut acro th ha rgonwhr t cool down to room tmratur. t can

xt a a homognou old oluton alha ha

btwn tmratur t and t Whn th alloy

gt to t th dcomoton of art of th old

oluton nto bta may not occur and ntad a

mtatabl old oluton wll rult h cor

rch ha may rctat out vry lowly at room

tmratur and Schwzr and Myr ( 1 978)uggt that th dcontnuou rctaton of

cor can b ud to tablh th authntcty of

ancnt lvr Thy xtraolat from xrmntal

data to gv a growth rat of about 1 0

mcron r

yar for th rat of rctaton h knd of

growth can lad to agmbrttlmnt of ancnt

mtal homon and Chattr ( 195) alo

found that lad formd at th gran boundar of

mur lvr and ld to mbrttlmnt

00% Cu


43/182

Twhasd ara

22

Fgure 3 Cu-Au ase agam.

Intemetllic Compound Fomton

When some metals are mxed together they canform phases that are essentaly lke ordnary

chemcal substances n that they are effectvely

compounds of xed composton An example s

the goldcopper alloys hese alloys were used n

antquty especally n the more base copperrch

compostons n South Amerca hs alloy was

known as tumbaga and was used wdey both for

castngs and for hammered sheework often

beng nshed by a depleton gldng process

(echtman 1973 Scott 1983; see g 39)

he dagram shows that copper and gold arecompletely souble n each other wth a eutectc-

type low metng pont whch occurs at a compo-

ston of 80 1 % gold at 9 1 1 C he rounded

shapes at the bottom o f the dagram show the

regons where the ordered phases can form here

are essentaly three dfferent ordered compos

tons: CAu CuAu and CuAu CuAu can

form beween about 85% to 9% gold It s a

superlattce formed by a pertetod (a sold state

T C

1 00% Cu

pertectc reacton) at about 0 C (Rhnes

Bond and Rummel 1 95 5) CAu can formbeween 50% and 50 8% gold CuAu can form

beween 70% to 85% gold

Ordered phases such as these have to be ds

tngushed from those phases normaly called

ntermetallc componds In termetalc com

pounds are usualy represented on the phase da

gram by a straght ne that passes down vertcaly

as the temperature falls here may be wo such

lnes close together that mark out a rectanguar

block on the phase dagram showng the areas

over whch the ntermetalc compound mayform he o rdered phases are rather dfferent

because they may be formed over wder compos-

tonal lmts they do not show vertcal phase

boundares n the form of straght lnes and they

may pass easly beween ordered regons and ds -

ordered regons

owever these ordered phases are usualy

harder than the d sordered alloy of the same com-

poston and they may make the process of

CuA 1 00% Au


44/182

igue 40 Cu-Pb phase diaga.

workng and annealng to hape more dcult.

For example the quenched alloy n the goldcopper ytem beween about 85% gold and 50%

gold are ofter than the alloy that are allowed to

cool lowly n ar. Th the oppote of the tu

aton that ext n alloy uch a ron and carbon

where the materal i dramatcally hardened by

quenchng becaue of the formaton of new

phae martente The reaon why goldcopper

alloy are ofter i that the quenchng proce up

pree the formaton of the ordered phae whch

need ome tme to form and t thee ordered

phae that gve re to higher hardne value andto the dculty ometme experenced n the

workng of thee goldcopper alloy. South Amer

can Indan n lowland Colomba for example

ued water quenching after annealng n order to

make the alloy eaier to work to hape and to

avod embrttlement

There are many example of ntermetallc

compound uch a cementte (FeC whch

contan 66% carbon and the delta phae n

bronze whch an intermetallc compound of

the formula C Sn

mmscble Stuctuesn ome cae metal may be completely noluble

n each other. Example of th type of mcro

tructure are hown by the alloy of copper and

lead zinc and lead and ron and copper A the

temperature fall from the melt of thee mutual ly

noluble metal one ofthem wll be precptated

Tw-phae Mateia

23

uually a globule of one phae n gran of the

hgher melting pont metal An example leadedcopper hown n Figure 0.

The dagram how that the mcrotructure

cont of wo dtnct phae and that the copper

gran that form wll contan globule of lead.

Practically all the copper wll old before the

leadcopper eutectc form. Thi leadcopper

eutectc for all practcal purpoe pure lead a

t conit of 999% lead and 0 1 % copper Th

mean that the lead egregated whle the olidi

caton proce takng place Ordnarly the

eparaton of lead globule would be expected toreult n mave egregaton and an unuable

materal would reult There a monotectc reac

ton at 95 5 c whch occur when the lqudfrom which the copper eparatng out reache a

compoton of3 6% lead. At thi pont a new liq

ud form that contan about 8% lead. Thi

new lqud heave than the rt lqud and o

t tend to nk under gravty owever n prac

tce the gro egregation i lmted by the forma

ton of a denditc tructure upon cating n the

copperrch alloy and wth a hgh cooling ratethe lead nely dpeed among the dendrte

Wth very hgh lead content alloy the two lq

ud that eparate out form an emulon when

they are cooled from about 1 000 C (Lord 1 99

Th emulon reult n a dvon nto vey ne

droplet o that gro eparaton cannot occur

Wth leaded copper bra or bronze alloy

the lead uually occur a mall nely dpered

_-

pointCu Cu

+

_

--

two lqu ds 1 084.5 c

36 95 C 87

Cu iqudeltngpont 326 C

Pb(3275 C)

Cu

Cu Pb (eutei of 999% Pb 0. % Cu )

Pb


45/182

wpha Mateia

24

hercal globle cattered at the gra bod

are ad wth the gra themelve Lead hathe effect of makg the alloy of coer eaer to

cat t ca for examle, mrove the dty of

the alloy the melt ead alo make coer

alloy eaer to work ce the lead act a a area

ofweake betwee the gra. h of o

ractcal e f the alloy ed for the mafac

tre of dagger or word blade ce they wll be

weakeed by the clo oflead, bt t adva

tageo for the rodcto of cat obect

t ot trctly tre that ro olble

coer the hae dagram more comlex thathat, althogh the ed relt of admxtre of

coer wth mall amot of ro the reece

of mall dedrte or globle of ro mxed wth

the coer gra. he hae dagram gve

Aedx G th book he coolg of a 6%

ro coer alloy examed by Cooke ad

Achebreer ( 95) A the 9% coer ad

6% ro alloy cool, t reache the lqd at

abot 115 C ad old gamma ro beg to

earate ot h gamma ro wll cota abot

8 3% coer old olto. A the temeratrefall, more of the gamma rorch hae earate

tl at 1095 C the rectatg ro cota

abot 8 5 % coer At the coerrch de of the

dagram the comoto of the tll lqd co

er follow the lqd tl at 1 095 C the coer wll cota omethg lke 3% ro

olto. At 1 08 .5 C, a ertectc reacto wll

occr betwee the lqd ad the rectated

gamma hae to gve a old olto of 96% co

er ad % ro h mea that gve a vey

low coolg rate the alloy hold cot of a

old olto (eta hae) of 96% coer ad

% ro wth redal gamma () ro artcle

A the temeratre fall, the coer gradally

rectated ot of the alha (e ro ad at theame tme the eta () hae loe ro acetecme, o far o evdece ha come to lght to

gget that the ertectc reacto had occrred

Becae of the reece o f alhahae ro (fer

rte), the coer alloy cotag ro are ally

ferromagetc ad ca ometme be cked

wth a maget.

Care mt be take whe grdg ad ol

hg leaded alloy to ere that lead globle

do ot dro ot (wthot otce beg take of

ther extece) the roce f they do fall ot,

they leave mall hercal hole ad t may thebecome vey dclt to dtgh betwee

oroty de to catg defect ad lead cl o

a a alloyg cottet, ce both aear a

hole the olhed ecto.


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4 HE MCRORUCURE OF N BRONZE

Some of the features to be found n alloys o f cop

per and tn commonly referred to as brone ormore correctly as tn brone have been dscussed

n prevous chapters The phase dagram for the

coppertn system s rather complex and cannot

be dscussed fully here and the one gven n ths

book gnores the owtemperature phase eld of

the alpha epslon phase regon Fg 33and Fgs 1 98 99 n Appendx G). hs s

because the phase never appears n bro nes of up

to abou 8% tn that have been manufactured by

conventonal means Thousands of hours of

annealng are necessary n order to make the phase appear and of course such condtons

never occur even n modern brones Despte

ths common forms of equlbrum dagrams

contan no clue that equlbrum s practcaly

never attaned Even more surprsngly some

modern metallurgcal textbooks appear to be

unknowledgeable on the subect and mantan

that an aloy wth % tn wl decompose on cool

ng from the usual alpha + delta regon to gvealpha and eta wthout dfculty!

Tn brones may convenenty be dvded nto

two regons lowtn brones and hghtn

brones Lowtn brones are those n whch the

tn content s less than 1 7% hs s the max-

mum theoretca lmt o f the solublty o f tn n

the copperrch sod soluton n practce the

usual lmt of sold soluton s nearer to 1 4%

although t s rare to nd a brone wth ths tn

content n a homogeneous sngle phase

When a tn brone s cast the alloy s exten

svely segregated usualy wth cored dendrtc

growth and an nll of the alpha

+delta eutectod

surrounds the dendrt c arms The center of the

dendrte arms are copperrch snce copper has

the hgher meltng pont and the successve

growth of the arms resuts n the deposton of

more t n At lowtn contents for example

between and 5% t may be possble for all the

tn to be absorbed nto the dendrtc growth Ths

vares consderaby dependng on the coolng rate

of the brone and the knd of castng nvolved f

th e coolng rate s vey slow there s a greaterchance of reachng equlbrum and the amount

of nterdendrtc delta phase wll be much

reduced or dsappear entrely owever at t ncontents of about 1 0% t s very unusual n cast

ngs from antquty to get absorpton of all the

delta phase and the dendrtes wll usualy be sur

rounded by a matr x of the alpha + delta eutectod

As the tn content ncreases the proporton of

nterdendrtc eutectod also ncreases fa homo

geneous coppertn alloy s worked by hammerng

and annealng then the typcal features seen n

facecentered cubc metals wl be developed;

namey anneang twns stran lnes progressvely ner grans as a result of workng and at

tened grans f left n the worked condton as

dscussed earler The same features wll develop f

the aloy s twophased athough the eutectod s

rather brttle and may be broken up to some

extent The usua mcrostructure shows the pres

ence of small sands of alpha + delta eutectodbetween the recystaled grans of the alpha sold

soluton f corng n the orgnal cast ngot was

pronounced then ths may be carred over n the

worked aloy as a fant or "ghost dendrtc pat

tern supermposed upon the recrystalled grans

When a brone secton s etched wth ferrc cho

rde ths dfference n alloy composton due to

corng may only be apparent as vague d erences

n shadng of the alloy and a dendrtc outne of

the shadng may be vey dcult to see Some

experence n the examnaton ofbrones must be

deveoped so that a worker can dfferentate

between uneven etchng and uneven colorng of

the specmen surface due to corng

Apart from compcatons ntroduced by

other alloyng elements such as nc the struc

tural features seen n most lowtn brones are the

followng

J omogeneous brones n whch all the tnhas dssolved wth the copper and whch do

not dsplay corng or resdual cast features.

2 Cored brones n whch there s an unequadstrbuton of copper and t n but no eutec

tod phase present

3Brones n whch both the alpha phase and


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e suu n Bn

2

the eueoid phae are preent.

4Bronze n whih the alpha phae i extenively ored and where the euteoid phae i

preent.

Mot anient alloy have le than 1 7% tin . At

thi level of n onen bronze an be old

worked and annealed; however, if the tin ontent

beween 1 % and 1 9% it ha been found that

the alloy i unworkable it an nether be hot

worked nor oldworked. A lm of delta form

and th brittle phae then oat the grain bound

arie with the reul that the alloy break up nopiee. However above 1 9% tin the bronze an

be hotworked. Bell and mirror in antiquity

were ofen made of ternay tin bronze oni ting

ofabout 05% tin 1 0% lead, the remainder

being opper. Alloy of th type were almot

invariably at. B inary tin bronze ontaining

more than 1 7% tin often have about 3% tin

whih orrepond loely o the equilib rium

value of he beta phae of the bronze ytem,

whh ha been mentioned in onnetion with

periteti tranformaion. Above 586 C abronze in the beta region an be readily worked

wherea ifallowed o ool lowly o room temper

ature he bronze would deompoe into alpha

and delta and be impoible o work. One advan

tage of beta bronze i hat the beta phae an be

retained by quenhing A omplete aount of

thi proe i quite omplex b u one ofthe mot

mportant poin i hat the beta phae i retained

by quenhing a a truture of marteniti nee

dle. Thi quenhed beta bronze i very hard but

a lot le britt le than the ame bronze lowlyooled o the alpha euteoid room temperature

form. Apart from a few at gur ine the maor

ty of artifat of beta bronze ompoition were

made by the following erie of operation he

alloy wa made up a aurately a the tehnology

of the time allowed a blank wa then at in the

approximate form of the deired obet, and the

obet wa haped by howorking at a tempera

ture of abou 650 C At the end of he working

proe the alloy wa uni formly reheated o about

the ame temperature and wa then rapidlyquenhed o preerve the hightemperature

phae and o produe a marteniti truture).

Hammer mark and oxde ale ould then beremoved by grinding with abraive of variou

grade, often on a imple lathe, and then the

obet wa polihed Surfae deoration, if

preent wa ut into the urfae with drill o r an

abraive wheel before nal polihing

Although ertain veel made from th i alloy

poeed interetng muial propertie the prin

ple reaon for it ue in region where tin wa

plentiful, wa it olor The olor of typial beta

bronze reemble gold Beta bronze were rt

found in ndia and Thailand from the early enturie and they pread lowly o the NearEat. The lami alloy white bronze, sadruy, i

an example of a hight in alloy. t wa alo found

in Java and Korea but when bra beame more

widely known, hightin bro nze ue beame muh

more limited

The alloy known a specuLum, whih may on

tain up o about 3 5% tin i aid by ome o have

been ued by the Roman for the manufature of

mirror However, Roman mirror were often

made by tinning; the alloy itelf wa often a low

tin bronze At high level of tin uh a thoe

enountered in tinned urfae the following

intermetalli phae of the oppertin ytem

mu be onidered arefully ( 1 ) the delta )

phae whih ha already been diued Cu Sn 8 'ontaining about 36% ti n; ) t he epilon )

phae CSn ontaining about 38 % tin; (3)

the eta ) phae ontaining 61 0% tin, CSn

Here , in t inned urfae, the epilon phae doe

appear and i important in undertanding the

mirotruture. When tin i applied o bronze,

layer of both the eta and the epi lon phae an

develop by interdiffuion between the bronze and

the molten tin, whih then an develop layered

truture in the following equene urfae tin

eta phae epilon pha e ubtrate bronze.

Under the optial miroope, tin i light and

ilvery in appearane the eta ompound i

lightly more greyblue in olor, the epilon phae

i the darket greyblue and the delta i light blue.

The range of feature that may form o n tinnedurfae i ompliated: CSn i ommon and i


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Fige 1 gh. Cas ogge pnfo Ian Bonze wih 3 7% i and 3% aseni. Eh FeCI x 120

Fig e 2 fa gh Chi ese asone inese bne of e 1 9henuy Bonze wi 8% i and %

lea Eh: FeCI x80

often msdescrbed as tn see Meeks 986).Many tn bronzes are leaded. Wth lowtn

bronzes ypcally castngs the lead does not aloy

wth the copper or tn and occurs as small globues

throughout the sructure. Some gravy segregaton

may take the lead down to the base or bottom of

the castng but generally n cast structures the ds

rbuton s ne and random.

Wth a hgher percentage of tn the structure

may become dcut to understand f lead s

present as well. Ths s especally true fthe bronzes

are quenched. There are severa Roman mrrors

made n bronzes approxmatng to 2.7% tn3. 2% lead, and 73. 7% copper. When quenched

from ntermedate temperatures, a very ne part

ce matrx develops that s dcult to resolve

under the optcal mcroscope. hs s due to the

very ne dsperson of the lead and the develop

ment o f a Wdmansttten sructure n the

bronzes. f quenchng of brones of beta compos

ton s not sucent to retan beta, then decompo

ston nto a Wdmansttten sructure ofne alpha

and delta may occur. Some Roman mrrors have

ths knd of sructure. he stuaton s even more

compcated n fact, because n leadedtn bronzes

the meltng ponts of the alloys are much lower

than n the bnary system. he ternay phase da

he Mirtructure in Bne

27

gram shows that the presence of wo lquds for

many compostons above 73 C may preventquenchng from temperatures hgh enough to

retan beta (see Appendx G Fg 2 J 2 .Fgure J shows a secton through a cast toggle

pn from Iran etched n FeCl at x50. he net

work of the a + 0 eutectod can cearly be seen nthe nterdendrtc regons. he togge pn has a

composton of92.3% copper, 3.7% tn 0.6%

znc, 0.% ron and 1 .3% arsenc. Note that theaphase (the copperrch component appears lght

n color except near the eutectod where some cor

ng occurs. The corng looks as though some of thetn s beng depeted n the regon of the a + 0eutectod as some tn from the a sold solutonregon mgrates to on up wth a he darkerregons around the a + 0 phases are copperrchcompared to the rest o f the bronze.

The bronze sructure of the ncense burner n

Fgure 2 s atypcal consstng of small polygo

na grans wth patches of the eutectod beween

them and nterspersed wth small globules oflead.

hs le

Metallography and Microstructure in Ancient and Historic Metals

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