A Systematic Approach to Bronze Corrosion Products

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A SYSTEMATIC APPROACH TO BRONZE CORROSION PRODUCTS

AND THE METHODS OF TREATMENT, APPLIED ON THREE

BRONZE ANKLETS FROM DHAMAR MUSEUM, YEMEN.

by Mohamed M. Megahed

Three bronze anklets, found during the archaeological excavation of Yemeni mission 2002 A.D., in Gabal al- lawd, Jawf area,

Yemen and, dated back to Minaean period in Yemen (sixth century B.C. – 24 B.C.),are now in Dhamar regional museum.

They suffered deterioration: two of these anklets had a thick corrosion products of pale- green/brown, the third had a

rust-colored Black and Brown with the presence of small parts and scattered pale green.

umerous studies on ancient and historical bronzes 2CuCl + H2O = 2HCl + Cu2O have tried to establish the chemical characteristics Nand structure of natural patinas grown on artifacts 7KHK\GURFKORULFDFLGJHQHUDWHGE\WKLVUHDFWLRQZLOOWKHQ H[SRVHGIRUORQJSHULRGVRIWLPHWRVRLODWPRVSKHUHZDWHU produce more cuprous chloride: or sea water. The long-term corrosion of bronzes is accom-

SDQLHG E\ VWUXFWXUDO WUDQVIRUPDWLRQV OHDGLQJ WR D VWHDG\ 2HCl + 2Cu = 2CuCl + H2 state. Different surface patterns have then been observed, depending on the corrosive environment (chemical compo- %XW0DFOHRG>@KDGSRLQWHGRXWWKDWWKH¨*RIUHDF- VLWLRQ3+UHVLVWLYLW\HWF EXWDOVRRQRWKHUQRQQHJOLJLEOH WLRQIRUHTXDWLRQLVNFDOPROHîVKRZLQJWKDWWKH parameters such as historical periods, metallurgical tech- UHDFWLRQ ZLOO QRW SURFHHG VSRQWDQHRXVO\ EHFDXVH RI WKH niques or even kind and size of the artifacts [1]. SRVLWLYH YDOXH RI ¨* ,Q VWDQGDUG FRQGLWLRQV WKH SRVLWLYH $QDO\WLFDOLQYHVWLJDWLRQVUHYHDOHGWKDWWKHPDLQFRUURGLQJ VLJQRIWKH¨*RIUHDFWLRQIRUWKHK\GURO\VLVRI1DQWRNLWH DJHQWLVUHSUHVHQWHGE\FKORULQHFRQWDLQLQJVSHFLHVWKDWLQ- means that the reaction cannot proceed as such without an GXFHWKHIRUPDWLRQRIGDQJHURXVFRSSHUFKORULGHVDQGR[\ DGGLWLRQDOWKHUPRG\QDPLFGULYLQJIRUFH,QDGGLWLRQ1DQ- chlorides at the interface between the metal surface and WRNLWHKDVDVROXELOLW\RIDERXWJSHUPORIZDWHU WKHRXWHUPRVWFRUURVLRQSURGXFWVOD\HUVYLDDFRQWLQXRXVO\ DWURRPWHPSHUDWXUHDQGWKLVORZVROXELOLW\OLPLWVWKHH[- RFFXUULQJUHDFWLRQ)RUPDQ\DUFKDHRORJLFDOREMHFWVWKHUH- WHQWWRZKLFKK\GURO\VLVUHDFWLRQVPD\RFFXU,WLVSRVVLEOH active cuprous chloride (Cu Cl) species is considered as the WRSURYLGHDWKHUPRG\QDPLFWKUXVWWRWKHULJKWKDQGVLGH principal agent of the so-called bronze disease, i.e. the pro- RI2UJDQ·VHTXDWLRQLIWKHSRVLWLYH¨*FDQEHRYHUULGGHQ cess of interaction of chloride containing species within the E\RWKHUIDFWRUV2QHRIWKHIDFWRUVWKDWPXVWEHFRQVLG- EURQ]H SDWLQD ZLWKPRLVWXUHDQGDLUDFFRPSDQLHGE\FRU- HUHGLVWKHSUHVHQFHRIDOOR\LQJHOHPHQWVWLQLQEURQ]HRU URVLRQRIWKHFRSSHUDOOR\LWVHOI7KHFXSURXVFKORULGHF\FOL- zinc in brass. There are, of course, electrochemical and FDOO\UHDFWVZLWK2[\JHQDQGDWPRVSKHULFZDWHU KXPLGLW\ NLQHWLF IDFWRUV WR EH FRQVLGHUHG KHUH 1RW RQO\ WKHUH DUH WKXVJLYLQJULVHWRWKHIRUPDWLRQRI$WDFDPLWH&X 2+ &O subtle electrochemical factors to be considered concerning DQG LWV SRO\PRUSKV 7KHVH R[\FKORULGH FRPSRXQGV UHDFW the difference in potential between tin-rich phases and the with copper to form cuprous chloride and water, and in this copper-rich alpha phase in bronzes, but there are a vari- ZD\ &X &O 2 DQG +2 DUH FRQYHUWHG LQ FXSULWH &X2 HW\RIEXULDOFRQGLWLRQVWREHFRQVLGHUHG>@7KHIRUPDWLRQ DQG$WDFDPLWH &X 2+ &O LQDF\FOLFDODQGFRQWLQXRXV RIWKHVHSDWLQDVLQEXULDOLVDVFULEHGWRR[\JHQDQGFDUERQ SURFHVV7KHÀQDOSURGXFWVRIWKHUHDFWLRQDUHOLJKWJUHHQ GLR[LGHFDUULHGE\JURXQGZDWHUV7KHVDOWVSUHVHQWLQVRLO SRZGHU\YROXPLQRXVEDVLFFKORULGHVRIFRSSHUZKLFKGLV- VROXWLRQVFDQLQÁXHQFHWKHIRUPDWLRQRIWKHSDWLQDDQGWKH UXSWWKHVXUIDFHDQGPD\GLVÀJXUHWKHDUWLIDFWV7KHQDWXUH nature of the corrosion, but on the whole are of minor im- DQGFRPSRVLWLRQRIWKHVRLODWWKHH[FDYDWLRQVLWHLVRIJUHDW portance. The dissolution of copper and other divalent ions importance for the degradation of the archaeological arti- LVVROHO\GXHWRWKHIUHHFDUERQGLR[LGHLQWKHZDWHUDQGWKH IDFWVEXWLQWKHFDVHRIPHWDOEURQ]HREMHFWVKXPLGLW\DQG progress of this dissolution is dependent on the concentra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,QKXPXVULFKVDQG\VRLOV with low lime content, there is no inhibiting effect on the decomposition of the patina to cre- DWH D WLQ R[LGH VXUIDFH while in lime containing soils, where the soil so- OXWLRQV PD\ FRQWDLQ FDO- cium bicarbonate, this decomposition is inhib- Fig. 3 - ME for a sample from the anklet A shows the LWHG>@ Uniform corrosion (50X). The purpose of the pre- VHQWSDSHULVWRVWDUWÀOO- ing the lacks diagnosed DERYH )LUVW E\ SURSRV- Fig. 1 - shows the location of Gabal- ing a suitable methodol- al lawd , Al-Gowf area ,Yemen. (After: RJ\IRUWKHVXUIDFHVWXG\ 5RELQ&%UHWRQ-)>@ of archaeological metals, WKHQ E\ IRFXVLQJ RQ EL- QDU\&X6QDOOR\VWRJHWDGHHSHULQVLJKWLQWRWKHSK\VLFDO and chemical characteristics of bronze patinas. This was DFKLHYHGWKURXJKDV\VWHPDWLFVWXG\IRUWKUHHEURQ]HDQ- NOHWVGDWLQJEDFNWRWKH0LQDHDQSHULRG VL[WKFHQWXU\%&WR Fig. 4 - ME for a sample from the anklet B shows the %& DQGIRXQGGXULQJDUFKDHRORJLFDOH[FDYDWLRQLQ Grieve corrosion (150X). $'LQ*DEDODOODZG$O*RZIDUHD ÀJ Fig. 5 - ME for a sample from the 0$7(5,$/6$1'0(7+2'6'(6&5,37,21$1'&21',7,21 anklet C, suffers The dimensions of the three anklets are similar in size and from pitting corrosion (50x). VFDOH WKH GLDPHWHU RI HDFK DQNOHW LV DERXW FP7KH\ suffered from the deterioration. The two others klets had DKHDY\FUXVWRISDOHJUHHQFRUURVLRQSURGXFWVLQFRUSRUDWLQJ VRLOSDUWLFOHVGLVÀJXULQJWKHPDQGOHIWWKHPXJO\ ÀJ

6&$11,1*(/(&75210,&526&23,&(;$0,1$7,21 6(0 6(0H[DPLQDWLRQRIWKHDQNOHWVVKRZHGWKHLUGHWHULRUDWHG VSRWVZKLFKGLVSHUVHGRQWKHPHWDODVLWLVVKRZQLQ ÀJV 7KLV FRQÀUPHG WKH UHVXOWV REWDLQHG E\ PHWDOOR- JUDSKLFH[DPLQDWLRQ

Fig. 6 - shows SEM examination for a sample from the anklet A, suffers from A B C pitting corrosion and distorted surface (200X ).

Fig. 7 - shows SEM examination for a sample from the anklet B, suffers from micro cracks & Grieve corrosion (1500X). )LJVKRZVWKHÀUVWVLGHRIWKHDQNOHWVEHIRUHWUHDWPHQW

(;$0,1$7,21$1'$1$/<6,6 7KH WKUHH DQNOHWV ZHUH H[DPLQHG E\ PHWDOORJUDSKLF DQG VFDQQLQJHOHFWURQ0LFURVFRSH&RUURVLRQSURGXFWVZHUHDQD- O\]HG E\ ;UD\ GLIIUDFWLRQ PHWKRG ;5' DQG WKH PHWDOOLF SRUWLRQE\;5)

0(7$//2*5$3+,&(;$0,1$7,21 0( ([DPLQDWLRQ RI WKH WKUHH DQNOHWV VKRZV WKH HORQJDWLRQ RI the metallic grains in the direction of hammering. this is in addition to the appearance of deteriorated spots dispersed RQWKHPHWDOVXUIDFHDVLWLVVKRZQLQ ÀJV Fig. 11 - Shows XRD scan for the corrosion products of the anklet C.

Fig. 8 - Shows SEM examination for a sample from the anklet C, suffers from pitting corrosion and distorted surface (500X).

;5$<',))5$&7,21$1$/<6,6 ;5' Three small samples were taken from the corrosion prod- XFWVPL[HGZLWKWKHVRLOUHVLGXHVFRYHULQJWKHDQNOHWVDQG DQDO\]HG E\ XVLQJ D 3KLOLSV ;UD\ 'LIIUDFWRPHWHU ZLWK &X .ŞUDGLDWLRQ7KHÀUVWVDPSOHZDVWDNHQIURPWKHUHGGLVK EURZQOD\HUWKDWFRYHUHGWKHDQNOHWQR$WKHVHFRQGVDP- ple was taken from the pale greenish crust that covering WKHDQNOHWQR%DQGWKHWKLUGVDPSOHZDVH[WUDFWHGE\WKH pale greenish crust that covered the surface of the anklet &7KHREWDLQHGGLIIUDFWLRQVFDQVDUHUHSRUWHGLQ ÀJXUHV QR DQGWKHLGHQWLÀHGFRPSRXQGVLQWDEOH ;UD\GLIIUDFWLRQSDWWHUQVRIWKHFRUURVLRQSURGXFWVRIWKH Tab. 1 - Shows XRD analysis results of corrosion products of the anklets. DQNOHWVLQGLFDWHWKDWWKH\FRQVLVWHVVHQWLDOO\RI$WDFDPLWH ;5$<)/825(6&(1&($1$/<6,6 ;5) Cu 2+ &O3DUDWDFDPLWH&X 2+ &ODQGFXSULWH&X2 ;5D\)OXRUHVFHQFHLVDQRQGHVWUXFWLYHSRZHUIXODQGHDV\ WRXVHWHFKQLTXHIRUWKHHOHPHQWDODQDO\VLVRIDZLGHYD- ULHW\ RI PDWHULDOV 7KUHH VPDOO VDPSOHV IURP WKH DQNOHWV ZHUHDQDO\]HGH[SORLWLQJWKLVWHFKQLTXHWRGHWHUPLQHWKHLU FRPSRVLWLRQ E\ XVLQJ D 1,721;/ 86$ GULYHQ ZLWK VRIWZDUHYHUVLRQ(7KHUHVXOWVVXJJHVWDEURQ]HDOOR\ with a high a mounts of Tin and traces from Lead, Iron and =LQFDVUHSRUWHGWDEOH

Tab. 2 - Shows XRF analysis results of the anklets.

75($70(17$1'&216(59$7,21 Fig. 9 - Shows XRD scan for the corrosion products of the anklet A. The use of chemical treatments for the anklets is more ac- ceptable than the mechanical cleaning, as these anklets KDG D WKLFN DQG FUXVW OD\HUV EHFDXVH WKH ORQJ SHULRG RI buried in the soil and the strong interaction between the VXUURXQGLQJ HQYLURQPHQW DQG WKH REMHFWV ,W ZLOO EH GLIÀ- FXOWWRUHPRYHWKHFRQFUHWLRQOD\HUVDQGWKHKDUGFUXVWVE\ PHFKDQLFDOWRROVZLWKRXWGDPDJLQJWKHVXUIDFHE\WKHSUHV- VXUHH[HUWHGGXULQJPHFKDQLFDOFOHDQLQJ,QDGGLWLRQDSUH- OLPLQDU\ H[DPLQDWLRQ SURYHG WKDW WKH DQNOHWV GLGQ·W KDYH DQ\ÀJXUHVRULQVFULSWLRQVRQWKHLUVXUIDFH6RWKHFKHPLFDO WUHDWPHQWZDVFKRVHQDVVLVWHGE\VNLOOHGPHFKDQLFDOFOHDQ- ing to remove the loose corrosion products. A serial of tests were carried out to determine which chemical compounds ZRXOGEHHIIHFWLYHZLWKRXWGDPDJHWKHREMHFWVWKHOHDVWE\ YDU\LQJWKHFRQFHQWUDWLRQDQGWLPHRIFRQWDFWLWZDVIRXQG the following chemical compounds are the least damaging Fig. 10 - Shows XRD scan for the corrosion products of the anklet B. and fastest acting solutions.

36 ArcheomaticA N°1 marzo 2014 Tecnologie per i Beni Culturali 37

The treatment procedures included the following steps:

6RDNLQJWKHDQNOHWVLQVROXWLRQRIVRGLXPKH[DPHW- aphosphate to convert the insoluble calcium carbonate in the encrustation to soluble salt which can be subse- TXHQWO\ZDVKHGDZD\7KLVZDVGRQHZLWKUHJXODUFKHFNV and removing loosened particles with silk brush. This SURFHGXUHZDVIROORZHGE\UHSHDWHGO\EDWKVRIGHLRQL]HG water with heating from time to time in order to loosen A B C WKHFRQFUHWLRQDQGKDUGOD\HUVRIWKHFRUURVLRQSURGXFWV This step resulted in dissolving and removing soil granules and the soluble corrosion products, and left the anklets KDYHDKDUGFUXVWRIYHU\DGKHUHQWFRUURVLRQFRPSRXQGV

The three anklets were soaked in alkaline Rochelle so- OXWLRQ WKDW ZDV FKDQJHG PDQ\ WLPHV DVVLVWHG E\ JHQWOH mechanical cleaning with silk brush from time to time to )LJ6KRZVWKHWKUHHDQNOHWV WKHÀUVWVLGH DIWHUWUHDWPHQW GLVVROYLQJWKHFRUURVLRQOD\HUVRIFRSSHU>,,@FRPSRXQGV .this step succeeded in removing green copper corrosion SURGXFWVDQGOHIWDUHGEURZQOD\HUFRYHULQJWKHDQNOHWV surfaces.

7RGLVVROYHDQGUHPRYHWKHR[LGHOD\HU>&XSULWH@VROX- WLRQRIVXOSKXULFDFLGZDVXVHGDVVLVWHGE\DEUXVKWRUH- PRYHWKHORRVHGOD\HUWKLVZDVGRQHZLWKUHJXODUFKHFNV DQGUHPRYLQJORRVHQHGOD\HUWKHVHSURFHGXUHVVXFFHHGHG in removing all the corrosion products.

After that the anklets were soaked in water and washed A B C E\DWRRWKEUXVKWRGLVORGJHUHVLGXHIURPFUHYLFHV

Repeated washing in hot deionized water altering heating DQGFRROLQJWRHQVXUHÁXVKLQJFDSLOODULHVWRUHPRYHDQ\ chemical residues.

Fig. 13 - Shows the three anklets (the second side) after treatment. 'U\LQJLQUHSHDWHGEDWKHVRIHWKHUIROORZHGE\GU\LQJLQ KRWVDZGXVWDQGPRSSHGGU\ZLWKVRIWFOHDQFORWK FXSURXVFKORULGHLVH[SRVHGWRWKHDWPRVSKHULFKXPLGLW\ )LQDOO\WKHDQNOHWVZHUHLVRODWHGZLWKSDUDORLG%GLV- F\FOLFDOO\UHDFWVZLWK2[\JHQDQGWKHZDWHUFRPLQJIURP VROYHGWROXHQHDQGWKH\ZHUHKDQGHGWR'KDPDUPX- the humid atmosphere thus gives rise to the formation of VHXP VHHÀJXUHV WKHJUHHQLVKDWDFDPLWH>&X 2+ &O@DQGLWVSRO\PRUSKV that reacts with copper to form new cuprous chloride 5(68/76$1'',6&866,21 DQG ZDWHU LQ WKLV ZD\ FRSSHU FKORULGH 2[\JHQ DQG It is worth noting that the selected Cu-based archaeologi- ZDWHU DUH FRQYHUWHG LQWR FXSULWH >&X2@ DQG DWDFDPLWH FDOREMHFWVKDYHEHHQSURGXFHGE\XVLQJWKHPDLQPDQX- >&X 2+ &O@LQDF\FOLFDODQGFRQWLQXRXVSURFHVVWKDW IDFWXULQJWHFKQLTXHVHPSOR\HGLQDQFLHQWWLPHWRSURGXFH FDQGLVÀJXUHWKHDUFKDHRORJLFDOREMHFWV>@ EURQ]H DUWLIDFWV 7KH VWXG\ GHFODUHG WKDW WKH DQFLHQW Yemeni manufacturer used both of casting and hammer- 0( 6(0 H[DPLQDWLRQV RI WKH WKUHH DQNOHWV VKRZ WKH ing technique to manufacture the three anklets. elongation of the bronze grains revealed the use of the KDPPHULQJPHWKRGLQWKH0DQXIDFWXUHRIWKHDQNOHWVDI- ;5'DQDO\VLVRIWKHFRUURVLRQSURGXFWVKDYHVKRZQWKH ter casting. presence of Copper and Tin species such as cassiterite [ 6Q2@FXSULWH>&X2@WHQRULWH>&X2@QDQWRNLWH>&X&O@ 7KLVSOD\HGDQHJDWLYHUROHLQWKHLUGHWHULRUDWLRQGXHWR DWDFDPLWH>&X 2+ &O@DQGSDUDWDFDPLWH>&X 2+ &O@ WKHH[LVWHGVWUDLQVLQVLGHWKHPHWDOOLFVWUXFWXUH,QDGGL- The latter compounds are basic copper chloride and are tion to the appearance of deterioration spots dispersed YHU\GDQJHURXVDVFRUURVLRQSURGXFWV>@7KHVDQG\VRLO RQ WKH PHWDO VXUIDFH UHSUHVHQW LQ 8QLIRUP FRUURVLRQ ZKHUH WKH WKUHH DQNOHWV ZHUH H[FDYDWHG SOD\HG DQ LP- dispersed on the surface of anklet A , Grieve corrosion portant role in their severe corrosion. This soil is a porous and the micro-crocks in the second anklet B, and micro- one changed from sub saturation to saturation with water, crocks with pitting corrosion which distort the surface of KDGGLIIHUHQWVDOWLRQVVSHFLDOO\WKHGDQJHURXVFKORULQH the third anklet C. ion [10,11]. This circulation of saline water in the soil had DVHULRXVHIIHFWRQWKHREMHFWVZKLFKOHGWRWKHIRUPD- 7KHVWXG\UHYHDOHGRQHW\SHRIFRUURVLRQSDWWHUQRQWKH WLRQRIWKHEURQ]HGLVHDVHFKORULGHFRPSRQHQWV>@ archaeological anklets. It was shown that the structure of WKHFRUURVLRQSDWWHUQLVFORVHO\OLQNHGWRWKHW\SHRIFRU- 7KHH[LVWLQJRIEURQ]HGLVHDVHZKLFKLVDGDQJHURXVF\- rosion process. A phenomenon common to the structure FOLFFRSSHUFRUURVLRQSKHQRPHQRQLQGXFHGE\WKHH[SR- LV GHFXSLÀFDWLRQ ,W ZDV DOVR VKRZQ WKDW WKH FRUURVLRQ sure to air of the reactive cuprous chloride [Cu Cl] species structure has several features: located inside the archaeological anklets. Indeed, when ([LVWLQJWKUHHOD\HUV H[WHUQDOFXSURXVR[LGHDQGLQWHUQDO 7KHH[WHUQDOOD\HUGXHWRDPRUHVHYHUHGLVVROXWLRQRI WKHDOOR\DVVRFLDWHGZLWKWKHSUHVHQFHRIVRLOHOHPHQWV A LQWKHLQWHUQDOOD\HU 5HODWLYHO\ODUJHDPRXQWRIFKORULGHVLQWKHYLFLQLW\RI the alteration front, which means the occurrence of mass transportation of chlorides from the soil to the metallic phase inward.

;5) DQDO\VLV LQGLFDWHG WKDW WKH DQNOHWV ZHUH PDGH RI EURQ]H DOOR\ >&X6Q@ WLQ ZDV IRXQG LQ D KLJK DPRXQW in the three anklets ,the percentage of it varied from >@DQGWKH\KDGDYHU\ORZSHUFHQWDJHRI /HDG,URQDQG=LQFDVSXULWLHVWKHVHSXULWLHVFRQWHQWV PD\FDPHIURPWKHXVHGFRSSHURUHVGXULQJH[WUDFWLRQ Also we can deduce that the ancient manufacturer recog- nized that the Lead isn’t valid to manufacture the anklets E\KDPPHULQJWHFKQLTXH B It must be noticed that in the case of artifacts found in archaeological soils, chemical composition and properties 3+ EXIIHU FDSDFLW\ RI VRLOV KDYH EHHQ PRGLÀHG ZLWK WLPH DQG WKDW ERWK FOLPDWH DQG D DFWLYLW\ RQ WKH VLWH have changed. It is obvious that the soil in which the artifacts were discovered cannot be regarded as the initial RQHLQZKLFKWKH\ZHUHOHIWRUEXULHG7KHQLQRUGHUWR GHÀQHDUHDOPHDQLQJRIDQDUFKDHRORJLFDOVRLOFRQGLWLRQ UHJDUGLQJ WKH FRUURVLRQ LW LV QHFHVVDU\ WR FRQVLGHU WKH VRLO PLFURPRUSKRORJ\ LQ RUGHU WR GHWHUPLQH WKH HYROX- WLRQV RI WKH VRLO FKDUDFWHULVWLFV VXFK DV GHFDOFLÀFDWLRQ PRGLÀFDWLRQRIEXIIHULQJFDSDFLW\>@

The choice of method for cleaning depends on what is UHTXLUHG IURP WKH REMHFW ZKDW LV PDGH RI DQG ZKDW condition it is in. The mechanical cleaning of metals is SUHIHUUHG PHWKRG IRU UHPRYLQJ GLVÀJXULQJ FRUURVLRQ ,W C allows more control and has less effect on the metal al- OR\-HGU]HMHZVND>@VXJJHVWHGWROHDYHVPDOOVWULSVRI FRUURVLRQ XQWRXFKHG E\ FOHDQLQJ LQ OHVV YLVLEOH SODFHV DVHYLGHQFHRIWKHVWDWHRIWKHREMHFWEHIRUH+RZHYHU the use of chemical treatments for the anklets is ac- FHSWDEOHWKDQWKHPHFKDQLFDOFOHDQLQJDVWKHVHREMHFWV KDGDWKLFNKDUGDQGFUXVWOD\HUVRIFRUURVLRQSURGXFWV PL[HGZLWKWKHGLUW\RIVRLOLWLVYHU\GLIÀFXOWWRUHPRYH LWE\PHFKDQLFDOPHWKRGVZLWKVXUIDFHVWKDWFDQEHHDV- LO\ GDPDJH E\ WKH SUHVVXUH H[HUWHG GXULQJ PHFKDQLFDO cleaning, besides the mechanical methods will create new points (pin Holes) for a new corrosion. Also if we OHDYHVPDOOVWULSVRIFRUURVLRQRUDWKLQOD\HURISDWLQDDV -HGU]HMHZVNDVXJJHVWHGWKHVHVWULSVZLOOEHFRPHDQHJD- tive electrode (Cathodic), whereas the metal under it, Fig. 14 - Shows the three anklets (A,B,C) after treatment. EHFRPHDQRGLFDQGLQH[LVWLQJDPRLVWXUHDVHOHFWURO\WH LPPHGLDWHO\D*DOYDQLFFHOOZLOOFUHDWHDQGWKHFRUURVLRQ process will start.

&21&/86,216 The information that can be derived from mineralogical the continued reactions giving rise to bronze disease before VWXG\RIDQFLHQWEURQ]HVKDVDGLUHFWLPSDFWRQWKHGHJUHH either all of the cuprous chloride is consumed or the humid- WR ZKLFK VXUIDFH FOHDQLQJ RI VXFK REMHFWV FDQ EH FDUULHG LW\OHYHOVLQSLWVRULQ]RQHVFRQWLJXRXVZLWKWKHVXUIDFHGURS RXWGXULQJFRQVHUYDWLRQ2QHRIWKHPRVWFXUUHQWO\IDYRUHG below levels required for continuous reaction. and best-informed approaches to their surface cleaning is to There is a strong interaction between the surrounding en- H[DPLQHWKHREMHFWFDUHIXOO\E\PRGHUQDSSDUDWXV YLURQPHQWDQGDOOR\DOVRWKHUHLVDVWURQJUHODWLRQEHWZHHQ ,WLVQHFHVVDU\WRFRQVLGHUWKHVRLOPLFURPRUSKRORJ\LQRUGHU WKHVXUURXQGLQJPHGLXPDQGVWUXFWXUHRIFRUURVLRQOD\HUV to determine the evolutions of the soil characteristics such The choice of method for cleaning depends on what is re- DVGHFDOFLÀFDWLRQPRGLÀFDWLRQRIEXIIHULQJFDSDFLW\ TXLUHGIURPWKHREMHFWZKDWLVPDGHRIDQGZKDWFRQGL- 7KHUHLVVWLOOPXFKWREHXQGHUVWRRGDERXWWKHFKHPLVWU\ tion it is in. DQGS+FRQGLWLRQVWKDWSUHYDLOLQEURQ]HREMHFWVDQGOHDGWR an accumulation of cuprous chloride in the corrosion prod- XFWV7KHFXSULFFRPSOH[HVPXVWSOD\DQLPSRUWDQWUROHLQ

38 ArcheomaticA N°1 marzo 2014 Tecnologie per i Beni Culturali 39

ABSTRACT BIBLIOGRAPHY THE AIM OF THIS PAPER IS TO EXAMINE, IN DETAIL, THE CORROSION OF THE SELECTED OBJECTS GROWN DURING THE LONG-TERM BURIAL AND IDENTIFY ITS PRODUCTS; THIS WILL HELP US TO UNDERSTAND THE CORROSIVE 5REELROD/%OHQJLQR-0HWDO 0RUSKRORJ\ DQG 0HFKDQLVPV RI FACTORS AND THE DEGRADATION MECHANISMS , AS WELL AS TO IDENTIFY THEIR CONSTITUTING METALS IN ORDER )RUPDWLRQRI1DWXUDO3DWLQDVRQ$UFKDHRORJLFDO9ROXPH1XP- TO CARRY OUT SCIENTIFIC TREATMENT AND CONSERVATION . EHUSS FOR THIS PURPOSE, SAMPLES FROM THE OBJECTS WERE EXAMINED BY METALLOGRAPHIC MICROSCOPE (ME) &DVDOHWWR03'H&DUR*0HWDO3URGXFWLRQRIUHIHUHQFH AND SCANNING ELECTRON MICROSCOPE (SEM), WHILE THE CORROSION PRODUCTS WERE ANALYZED BY X-RAY DQFLHQW&XEDVHGDOOR\VDQGWKHLUDFFHOHUDWHGGHJUDGDWLRQPHWKRGV DIFFRACTION (XRD). X-RAY FLUORESCENCE( XRF) WAS USED TO DETERMINE THE BULK ELEMENTS OF THE 0DWHULDOV6FLHQFH SURFHVVLQJ$SSOLHG3K\VLFV$SS OBJECTS. 2UJDQ 507KH ([DPLQDWLRQ$QG7UHDWPHQW2I %URQ]H$QWLTXL- XRD DATA SHOWED THAT THE CORROSION PRODUCTS ARE CUPRITE , ATACAMITE AND PARATACAMITE , WHE- WLHV,Q5HFHQW$GYDQFH,Q&RQVHUYDWLRQ%XWWHUZRUWK REAS XRF ANALYSIS POINTED OUT THAT THE ANKLETS ARE COMPOSED BY A BRONZE ALLOY. MICROSCOPIC 0DFOHRG , ' &RQVHUYDWLRQ 2I &RUURGHG &RSSHU$OOR\V$ FRP- EXAMINATION REVEALS THAT THE THREE ANKLETS SUFFERED DETERIORATION MAINLY IN SPOTS. EXPLOITING THE SDULVRQ2I1HZ$QG7UDGLRQDO0HWKRGV)RU5HPRYLQJ&KORULGH,RQV COLLECTED INFO, CHEMICAL CLEANING WAS CHOSEN FOR TREATING THE OBJECTS. 6WXGLHV,Q&RQVHUYDWLRQ 6FRWW$'%URQ]H'LVHDVH$UHYLHZRIVRPHFKHPLFDOSUREOHPV DQG WKH UROH RI UHODWLYH KXPLGLW\ 9ROXPH 1XPEHU DUWLFOH KEYWORDS SS BRONZE OBJECTS; CORROSION; SEM; XRF; XRD; TREATMENT; CONSERVATION 6FRWW$'$QH[DPLQDWLRQRIWKHSDWLQDDQGFRUURVLRQPRUSKR- ORJ\ RI VRPH 5RPDQ EURQ]H -$,& 9ROXPH 1XPEHU DUWL- FOHSS AUTHOR 5RELQ&%UHWRQ-)/H6DQFWXDLUH3UHLVODPLTXHGX*DEDODO MOHAMED M. MEGAHED Lawd, Nord -Yemen, Dans Academie des inscriptions et Belles Let- WHUV)UDQFHSS CONSERVATION DEPARTMENT, FACULTY OF ARCHAEOLOGY, FAYOUM UNIVERSITY, EGYPT. )MDHVWDG0HWDO7KHGHFD\RIDUFKDHRORJLFDOFRSSHUDOOR\DUWL- [email protected] IDFWVLQVRLOLQ0HWDO-DPHV/7'/RQGRQ 9DURXIDNX*HWDO&RUURVLRQRIDQFLHQWEURQ]HV0HWDOOXUJLD 9ROXPH1XPEHU 7\OHFDWH5)7KHHIIHFWRIVRLOFRUURVLRQRQORQJWHUPFRUURVLRQ of buried tin bronzes and copper, Journal of Archaeological Science, 1R (/0RZHOKL10+DPGL+7KHVRGLFVRLOVLQ(J\SWLQ0LQH- UDORJLFDOFKDUDFWHUL]DWLRQ(J\SW-RXUQDORI6RLO6FLHQFH9ROXPH 1XPEHU :HUQHU*HWDO&RUURVLYHGHFD\RIDUFKDHRORJLFDOPHWDOÀQGV IURPGLIIHUHQWVRLOVDQGHIIHFWVRIHQYLURQPHQWDOSROOXWLRQLQ0HWDO SURF RI WKH ,QWHUQ &RQI RQ 0HWDOV FRQVHUYDWLRQ )UDQFH SS 7HQQHQW1+ $QWRQLRN0%URQ]HGLVHDVHV\QWKHVLVDQG FKDUDFWHUL]DWLRQRIERWDOODFNLWHSDUDWDFDPLWHDQGDWDFDPLWHE\,Q- IUDUHGVSHFWURVFRS\LQ,&20&RPPLWWHHIRU&RQVHUYDWLRQWKWULHQ- QLDO0HHWLQJ2WWDZD3DULV ,QJR*0HWDO/DUJHVFDOHLQYHVWLJDWLRQRIFKHPLFDOFRPSR- sition , structure and corrosion mechanism of bronze archaeological DUWLIDFWV IURP 0HGLWHUUDQHDQ EDVLQ$SSOLHG 3K\VLFV$ 0DWHULDOV VFLHQFH SURFHVVLQJSS 5REELROD/%OHQJLQR-0HWDO2S&LWS -HGU]HMHZVND+$FRUURGHG(J\SWLDQ%URQ]H&OHDQLQJ$QG'L- VFRYHULHV6WXGLHV,Q&RQVHUYDWLRQ9ROXPH

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