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Journal of Cultural Heritage 14 (2013) 261–269

Available online at

www.sciencedirect.com

ase study

ombined in situ micro-XRF, LIBS and SEM-EDS analysis of base metal andorrosion products for Islamic copper alloyed artefacts from Umm Qais museum,ordan

beer Arafata, Maram Na’esb,∗, Vicky Kantarelouc, Naseem Haddada, Anastasia Giakoumakid,asilike Argyropoulose, Demetrios Anglosd,f, Andreas-Germanos Karydasc,g

Royal Scientific Society (RSS), 11941 Amman, JordanInstitute for Optics and Atomic Physics, Technical University of Berlin, EW 3-1, Hardenbergstr. 36, 10623 Berlin, GermanyX-ray Spectrometry Laboratory, Institute of Nuclear Physics, (NCSR) “Demokritos”, Aghia Paraskevi, 15310, Athens, GreeceInstitute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas (IESL-FORTH), P.O. Box 1385, 71110 Heraklion, GreeceTechnical and Educational Institute of Athens (TEI), Department of Conservation of Antiquities and Works of Art, Ag. Spyridona, 12210 Athens, GreeceDepartment of Chemistry, University of Crete, P.O. Box 2208, 71003 Heraklion, Crete, GreeceNuclear Spectrometry and Applications Laboratory, International Atomic Energy Agency (IAEA), Agency’s Laboratories Seibersdorf, A-2444, Seibersdorf, Austria

a r t i c l e i n f o

rticle history:eceived 13 February 2012ccepted 12 July 2012vailable online 25 August 2012

a b s t r a c t

Selected copper alloy artefacts from the collection of the Umm Qais museum at Irbid, Jordan, were stu-died by SEM-EDS analysis, while in situ analyses were performed by means of portable �-XRF and LIBSspectrometers. Analysis and characterization of base metal and corrosion products of the copper alloyed

eywords:ROMETmm Qaisopper alloy

artefacts were performed in relation to the environmental conditions of the display and as part of theoverall assessment of the museum environment. Findings of this study are directed towards guiding apreventive conservation strategy for the copper alloyed artefacts at the Umm Qais museum.

© 2012 Elsevier Masson SAS. All rights reserved.

ortable �-XRFortable LIBS

. Introduction

.1. Research aims

The present work aims to investigate the state of preservationnd manufacture technology of a collection of Islamic copper arte-acts from the Umm Qais archaeological site in Jordan. In particular,he study provides an insight on the usefulness and practicality ofortable micro-XRF and LIBS techniques for a spectroscopic based

dentification of metal corrosion products, including an evaluationf their analytical possibilities and limitations. Finally, the studyims to assess the environmental impact on the studied metal-ic artefacts and to provide recommendations on best practices toupport their better preservation.

∗ Corresponding author.E-mail address: maram@physik.tu-berlin.de (M. Na’es).

296-2074/$ – see front matter © 2012 Elsevier Masson SAS. All rights reserved.ttp://dx.doi.org/10.1016/j.culher.2012.07.003

1.2. The project

Within the framework of the three and a half year EUproject, PROMET1, extensive analytical characterization of metallicartefacts from eleven Mediterranean partner countries was under-taken. The project’s principal aim has been to ensure the survivalof the outstanding metallic collections throughout the Mediter-ranean region, covering the period from 3rd century BC to 20thcentury AD. The project connected 21 research institutions, cul-tural entities such as museums and conservation centres througha joint collaboration exploiting knowledge, equipment and mate-rial resources. Analysis, monitoring and conservation strategieswere developed during the project. A key objective and achieve-ment of PROMET was the development/optimization of portableMicro X-Ray Fluorescence (�-XRF) and Laser-Induced Breakdown

Spectroscopy (LIBS) spectrometers and relevant analytical appli-cations in the analysis of metal artefacts. The Institute of NuclearPhysics at the National Centre of Scientific Research “Demokritos”

1 PROMET, PROtection of METals, EU 6th FP INCO project, Contract no. 509126,www.promet.org.gr.

2 ltural

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optimized analytical performance, namely:

62 A. Arafat et al. / Journal of Cu

INP-NCSRD) and the Foundation for Research and Technology-ellas (IESL-FORTH), have used their portable micro-XRF and LIBSquipment respectively in an analytical campaign at Irbid-Jordano analyse non-destructively Islamic copper alloyed artefacts fromhe collection of Umm Qais museum, selected as a case study in theramework of PROMET by the Jordanian partner, the Royal Scientificociety (RSS).

.3. The case study

Metallurgy in eastern Mediterranean has developed signifi-antly during the Islamic period [1]. The multicultural remains ofhe Umm Qais (or Gadara) archaeological site, especially Islamic,omprise a large metallic collection that is mainly copper-based.he excavations took place between 1990 and 2003 whereas theajority of the metal objects studied in this project were found inugust 2001 in the excavation undertaken by the Department ofntiquities of Jordan. The collection selected in this work exem-lifies a representative sample of copper-based artefacts studieduring the conservation survey carried out by RSS on the metal-

ic collection at the Umm Qais museum [2]. The non-destructivenalysis of object’s composition and corrosion materials signi-es better understanding of their condition. Furthermore, theesults of this study enabled to associate the extent or absencef deterioration phenomena (e.g., bronze disease) not only on thenvironmental conditions but also on the chemical composition ofhe alloy.

.4. The site

Umm Qais is situated 110 km north of Amman on a broadromontory 378 meters above sea level with a strategic locationiewing the Yarmouk River, the Golan Heights, and Lake of Tiberias.t is known as Gadara, one of the most impressive Greco-Romanecapolis cities, and according to the Bible, the spot where Jesusast out the Devil from two demoniacs (mad men) into a herdf pigs (Mathew 8:28–34). The site has various remains from theoman, Greek, Byzantine, Umayyad, Mamluk and Ottoman periods.etallic artefacts compose around 13% of the archaeological

ollection at Umm Qais museum, the majority of which is copper-ased.

. Methodology

.1. Selection criteria

The museums in Jordan and in the Mediterranean areancounter a challenge in reducing the environmental impact onheir collections. In Jordan and in particularly at Irbid, environmen-al conditions have been rather unstable and with a considerablehange of atmospheric pollutants in addition to fluctuations in tem-erature and relative humidity [3], therefore not always suitable forisplaying specific material without control. Albeit many efforts in

ordanian museums, storage and display facilities are insufficient.t the Umm Qais museum the showcases are wooden and have noteen assessed for possible emission of volatile organic compoundsotentially reacting with the metal objects.

The selection criteria for the studied objects have been in prio-ity order as follows: composition (copper-based), date (Islamiceriod), display conditions (potential environmental influence),nd finally risk assessment (demanding conservation treatment).ccording to these criteria, ten objects were selected and are

escribed in chronological order in Table 1. Copper alloy arte-acts from the Islamic period present a substantial part of metallicollections in Jordanian museums. At the Umm Qais museum,ore than 85% of its metallic collection is copper-based. The date

Heritage 14 (2013) 261–269

and composition of the selected samples are representative toa wide range of Islamic metallic artefacts at Umm Qais. Cop-per metallurgy for civil and military uses had emerged in theIslamic periods, which the selected objects refer to (Umayyad toOttoman).

2.2. Assessment strategy

Selected objects have been visually assessed for their currentconservation condition. However, corrosion products are clearlyseen on most of the objects, while pitting is observed on a few ones.It is worth mentioning that studied artefacts have not been sub-jected to any chemical treatment previously. Table 1 summarisesthese preliminary observations. The objects are all on display atthe Umm Qais museum gallery. Environmental conditions at themuseum gallery were noticed to fluctuate frequently besides theabsence of any control for the showcases themselves. Therefore, anenvironmental monitoring of ambient conditions in the gallery wasperformed by the RSS team.

In situ non-destructive scientific analysis has become a prio-rity in studying historic and artistic works. For metallic objects, theheterogeneous distribution of corrosion products on surface andin-depth represents a major challenge in addition to the intricatechemical composition of copper corrosion products [4–9]. Chemi-cal characterisation by means of elemental analysis was conductedin order to identify the composition of original and corroded mate-rials. Analysis was performed with due consideration to heritagematerial integrity and significance, hence non-invasive portable�-XRF and micro-destructive LIBS spectroscopic techniques wereused. A Scanning Electron Microscopy - Energy Dispersive X-RaySpectrometer (SEM-EDS) was used too before the portable equip-ment became accessible [7–14].

3. Experimental

3.1. The National Centre of Scientific Research “Demokritos”(NCSRD) portable �-XRF spectrometer

The INP-NCSRD acquired a customized version of the ARTAXportable micro-XRF spectrometer (Bruker-AXS). The spectrometerprobe consists of an X-Ray micro focus Rh-anode tube (spot size50 �m × 50 �m, 50 kV, 1 mA, 30 W maximum power consumption,Be window 0.2 mm thickness) and a polycapillary X-Ray lens as afocusing optical element (IfG) [6]. The X-ray lens gain factor variesin the range of 3625 - 4900 - 1200 for exciting energies in theintervals 3–5, 10–15 and 25–30 keV, respectively, offering a spa-tial resolution of about 40 �m (@ 17.4 keV) and 70 �m (@ 6.4 keV),The X-Ray detection chain consists of a thermo-electrically cooled10 mm2 silicon drift detector (X-Flash, 1000B) with FWHM equal to146 eV (@ MnK� and 10 kcps) coupled with a digital signal proces-sor. The colour CCD camera offers live documentary image of theanalysed spot, whereas together with a dimmable white LED forsample illumination and a laser beam the reproducible position-ing of the measuring probe with respect to the analysed surfaceis assisted. Further on, the relatively large focal distance of theX-ray lens (21.2 mm) helps to analyse objects with irregular surface.(Fig. 1a).

The micro-XRF spectrometer has been developed to provide an

• dual detection of medium atomic number elements (e.g. Sn)through their K and L series of characteristic X-ray lines;

• detection of low atomic number elements by flashing Helium inthe air-path between sample and x-ray detector.

A. Arafat et al. / Journal of Cultural Heritage 14 (2013) 261–269 263

Table 1Narrative and preliminary condition assessment of studied copper alloyed artefacts from Umm Qais (Irbid, Jordan) and are displayed at Umm Qais Museum. (N.B. Umayyadperiod: 661-750AD; Mamluk period: 1250-1517AD; Ottoman period: 1516-1918AD.)

Object Code Object Serial Number Date Description Expected ManufacturingTechnology

Dimensions (mm) Condition

1 307 Umayyad Metallic jug with handleand long neck

Blowing + casting + forging Ømax = 10.8 cm Repaired and in a goodstate

e = 0.5 cmH = 16.4 cm

2 346 Umayyad Metallic jug with handlebroken and conserved

Blowing + rolling Ømax = 15 cm The handle was brokenand repaired

e = 0.3 cm Good stateH = 22.6 cm

3 347 Umayyad Metallic jug Blowing Ømax = 17.4 cme = 0.1 cmH = 24.5 cm Heavily corroded and

perforated

4 208 Late Mamluk/early Engraved bracelet Rolling + casting + forging Ømax = 5.8 cm In good stateOttoman e = 0.5 cm

5 216 Ottoman Bracelet with roundedcross section

Casting + rolling Ømax = 6 cm Presence of some activecorrosion (pitting)

e = 0.1–0.5 cm

6 210 Ottoman Twisted bracelet Forging + rolling Ømax = 5.8 cm In good statee = 0.5 cm

7 317 Ottoman Bracelet with flat crosssection

Rolling + casting + forging Ømax = 6.1 cm In good state

e = 0.35 cm

8 320 Ottoman Twisted and engravedbracelet

Rolling + casting Ømax = 5 cm Presence of activecorrosion (pitting)

e = 0.5 cm

9 327 Ottoman Heart shape metallicobject

Forging Area = 22 cm

e = 0.2 cm Presence of activecorrosion (pitting)

10 323 Late Ottoman Ring Rolling + casting + forging Ømax = 2 cm In good state

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According to curator records at Umm Qais museum.

The effective excitation of medium atomic number K-lines ischieved by mean of an appropriate polycapillary X-ray lens whichespite its high energy cut-off function enables the transmissionf adequate flux of energetic X-rays to detect minor amounts ofn. Since there is a particular interest for the analysis of Cu basedlloys, an experimental methodology was carried out to minimizehe incomplete charge collection generated below the intense Cueaks and thus to improve the sensitivity for S and Cl detection.he approach was based on the measurement of the intensity ofhe CuK� versus background (in the region 2-3 keV) at differ-nt positions of the X-ray detector with respect to the sampleurface. The decrease of the incomplete charge collection contri-ution to the spectral background is attained due to the restrictionf the exposed area of the X-ray detector to the fluorescenceadiation.

For the analysis of the bare metal of an artefact an appro-riate stratified filter is inserted in the exciting beam path, betweenhe X-ray source and the sample. The filter prevents the recordingf diffraction peaks in the energy spectrum which might inter-ere with elements characteristic X-rays and allows the detectionf trace impurities in the base metal. For the analysis of corro-ion products an unfiltered exciting beam is preferred so that tottain an optimum analytical range for major-minor elements,hereas in this case the detection of trace elements is not so impor-

ant. However, it should be also noted that the Helium flush wasot used during the in situ measurements at Irbid due to logis-ic difficulties for the transportation in Jordan of a pressurized Heank.

e = 0.3 cm

3.2. The Institute of Electronic Structure and Laser, Foundationfor Research and Technology - Hellas (IESL-FORTH) (IESL-FORTH)portable Laser-Induced Breakdown Spectroscopy (LIBS)spectrometer (LMNT-II)

In the framework of PROMET, substantial development onmobile LIBS technology was achieved at IESL-FORTH and a portableprototype instrument was produced. This prototype, LMNT-II,has been tested in various campaigns investigating archaeolo-gical metal objects at the Museum of Ancient Messene (Greece),at the National Museum at Damascus (Syria) and at the Numis-matic Museum of Yarmouk University (Jordan). The results wereencouraging, demonstrating the potential of portable LIBS as a use-ful tool in the conservation laboratory for identifying different typesof metal alloys and assessing the degree of corrosion on museummetal objects.

LMNT-II comprises a hand-held probe that includes the laserhead, optics to guide, attenuate and focus the laser beam on thesample. Optical emission from the plasma is collected through thehead and transmitted with an optical fibre to the spectrometerwhich along with a delay unit and the laser power supply, arehoused in the main unit. The laser emits 8 ns pulses at 1064 nmwith energy up to 15 mJ/pulse, which upon focusing probe a spotwith diameter around 200 �m on the surface of the object. The

spectrograph (HR4000, Ocean Optics Inc.) covers a spectral rangebetween 270 and 650 nm with spectral resolution of about 0.5 nmand uses a 3648 pixel CCD-array detector. The analysis is performedby positioning the probe head at the proper distance from the

264 A. Arafat et al. / Journal of Cultural

Fig. 1. a: the portable �-XRF analyzing in situ metallic artefact from Umm Qaismuseum, Irbid, Jordan (©PROMET 2008); b: the portable Laser-Induced Break-dFa

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own Spectroscopy (LIBS) developed by Institute of Electronic Structure and Laser,oundation for Research and Technology - Hellas (IESL-FORTH) analyzing metallicrtefact from Umm Qais museum, Irbid, Jordan (©PROMET 2008).

bject (defined by a special spacer). To ensure stability and accurateiming, the probe head is mounted on a small stage that permitsovement at the XYZ directions [7]. A visualisation camera enables

he user to have a view and save a snapshot of the area analysedFig. 1b). The emission from the plasma produced is recorded in

time-integrated mode by the spectrometer, which is fully con-rolled by a laptop PC.

.3. The Royal Scientific Society (RSS) Scanning Electronicroscopy - Energy Dispersive X-Ray Spectrometer (SEM-EDS)

The Royal Scientific Society used a Scanning Electron Micro-cope (Zeiss DSM 950) coupled with an Energy Dispersive X-raypectrometer (EDS, Tracor Northers). For objects with large sizeNo. 307, 346, 347), minute samples were taken for analysishile for the other objects no samples were taken and analysisas performed directly on the object. If needed, object’s surfaceas slightly grinded for analysis to reduce the interference and

ontamination from the surface corrosion layers.

. Results and discussion

.1. Environmental monitoring

The display environmental conditions in the museum werenvestigated and correlated with the conservation status of studied

Heritage 14 (2013) 261–269

objects as an indicative example for environment-condition rela-tionship at the Umm Qais museum. The environmental monitoringperformed by the RSS for one calendar year in the exhibitionhall of the Umm Qais museum where the objects were displayed(26 September 2006–30 August 2007). Monitored environmentalparameters included relative humidity (%RH) and ambient tem-perature (AT) in addition to some gaseous pollutants includingsulphur dioxide (SO2), nitrogen dioxide (NO2), ammonia (NH3)and Total Volatile Organic Compounds (TVOC). A Lufft traditionalmechanical temperature/humidity recorder was placed in themuseum hall to record ambient temperature and relative humidityonto paper charts. Seasonal monitoring was carried out by RSSfor three hours each time using a multi gas analyser and the SO2,NO2 and NH3 gases were analysed using the Electrochemical CellsMethod, while the TVOC by a portable gas analyser equipped witha Photo Ionisation Detector.

The monitoring results show that NH3 gas decreases with tem-perature increase with a highest concentration of 1 ppm in Januaryand February (winter season). NO2 didn’t reach above 0.1 ppm allyear round neither does it show an influence by AT and/or RH.SO2 had only a sudden increase on May then a sharp decrease inSeptember with almost steady value in between. This seems relatedwith the high tourist summer season besides the relatively higherRH 55% compared to the rest of the year. Higher humidity suspendsSO2 gas in the air and on surfaces, which may affect corrosion pro-cess of metallic artefacts. TVOC show quite a high concentrationbetween February and June that reaches up to 21 ppm, and tendsto increase with temperature increase and RH decrease. AverageAT was 26 to 30 ◦C and 10 to 14 ◦C in summer and winter seasons,respectively, while RH was 40 to 55% all year around.

According to Thomson (1986) [15], the levels of SO2 and NO2air pollutants are recommended not to exceed 3.8 × 10−3 ppmand 5.3 × 10−3 ppm, respectively. The Ghazawi’s environmentalstudy (2001) [3] shed light on the Umm Qais museum atmosphereperforming systematic measurements of AT and RH for five con-secutive months (February to July 2001). The study emphasised thenegative impact of the continuous opening of doors and windows,the direct exposure of artefacts to sunlight, as well as air pollutionpossibility, though the latter was not measured.

4.2. Materials and technology

The analytical results in association to the object’s date, func-tion and manufacturing process show that object’s technology isdependant on all these three factors. According to SEM-EDS analy-sis of base metals (Fig. 2a), copper amounts to approximately 75%of the Umayyad jars’ composition (objects number 307 and 346),while lead to 13 to 15%. Tin ranges between 7-9% and zinc between1 to 2%. Lead percentage decreases sharply down in the Ottomanbracelets (objects number 208, 216, 210, 317, 320) and in the heart-like object (no. 327) with a maximum of 2.2%, whereas tin alsoappears with only 1.2% as maximum value. On the contrary, zincshows relatively high percentages of concentration (12–35%) com-pared to the Umayyad jars and of the late Ottoman ring (no. 323).In particular, the late Ottoman ring has different visual appearance,texture and the chemical composition of a quaternary alloy (83% Cu,3% Pb, 5% Sn and 8% Zn). The Umayyad jug (no. 347) shows accordingSEM-EDS analysis almost 99% of Cu and traces of Zn.

In terms of original technology and function, copper alloys pro-vide materials with a wider range of physical, mechanical andchemical properties. Generally, alloying elements increase cop-per alloy strength, decrease its electrical conductivity, and alter

its colour [16]. The addition of lead increases alloy’s workabilitybut on the other hand its toxic nature limits its use, which in turnprovoked the use of bismuth as a safer alternative [16]. The addi-tion of zinc to copper forms a brass alloy, as zinc content increases,

A. Arafat et al. / Journal of Cultural

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SEM-EDS) and micro-XRF analysis results for the base metal of the measured Culloy artefacts; b: quantitative SEM-EDS analysis results for the green corrodedayers of the measured Cu alloy artefacts.

rass becomes yellower. Yellow brasses that contain up to 38% zincre referred to as �-brasses or single-phase copper-zinc alloys asefined in the Cu-Zn equilibrium phase diagram [17]. The Ottomaneriod (1516–1918) involves extensive trade with Europe for cen-uries including the 18th century, the time at which gold-colouredrass became more familiar in Europe as a cheap alternative for gold

ewellery [1,16]. Over half of the objects studied in this campaignave been used as golden-colour bracelets. Their major alloyingetals added to copper are Sn, Zn and Pb, which facilitate rolling,

wisting and casting techniques.Copper-tin alloys or bronzes are reddish in colour and can be

haped by hammering. Bronzes that contain up to 14% tin areeferred to as �-phase or single-phase copper-tin alloys as definedn the Cu-Sn equilibrium phase diagram [17].

According to the SEM-EDS results confirmed also by the portableicro-XRF analyses on cleaned small surface areas and the most

ommonly used categorization for copper alloys, it is possible tolassify the analysed objects into five groups, a copper alloy (no.47), leaded bronze (no. 307, 346), leaded brass (no. 208, 210, 317),rass (no. 216, 320, 327) and leaded gunmetal (no. 323).

.3. Corrosion products

The results of the SEM-EDS analysis and of the in situ appli-

ation of micro-XRF/LIBS techniques on different corrosion layerser analyzed object are presented in Table 2. The detected ele-ents by the micro-XRF and LIBS analysis are categorized as major

ma), minor (mi) and trace (tr) elements based on their relative

Heritage 14 (2013) 261–269 265

intensities with respect to Cu and incorporating in this semi-quantitative assessment the elemental response of each spectro-meter. The SEM-EDS results reflect the composition of a minutematerial extracted from a single corroded layer (green for theobjects no. 307, 347, 208, 216, 210, 317, 320 and 327, and red forthe objects 323 and 346). These quantitative results are presentedseparately in Fig. 2b. For the most of the green areas a rather simi-lar elemental pattern is observed; the presence of chlorine and thedepletion of the Cu alloying elements (such as Sn or/and Zn). We canalso observe an inhomogeneous distribution of S and Cl in corro-sion products that it is associated most likely with the surroundingenvironment, both the burial and post-excavation one.

The SEM-EDS analysis and the portable micro-XRF and LIBStechniques provide only elemental analysis with different ana-lytical range and sensitivity and cannot serve towards a definiteidentification of the corrosion compounds. However, the results ofthe elemental analysis in association with the colour observed andin reference to the known copper minerals and relevant corrosionproducts [18–22], can support and lead to specific suggestions. Thecomparison of the bare metal spectrum with respect to the oneproduced by the corrosion product is a recommended analyticalstrategy since it can demonstrate clearly elemental surface enrich-ment or depletion and thus to reveal the pattern of elements whichare in clear association with the corrosion products. A statisticalcorrelation between the colour of bronze corrosion products andtheir chemical composition has been proposed for outdoor bronzes[23].

For the leaded bronze 346 (#2) object characteristic micro-XRFand LIBS spectra from the base metal and the green/red-corrodedareas are presented in Figs. 3a–c and d–f, respectively. The pat-tern of the micro-XRF and LIBS spectra amongst the different areasreveal the predominance of key elements associated with corrosionproducts, such as Cu, Cl and Pb in the green area and Cu, Pb in thered one (Table 2).

The results of the elemental analysis of the corrosion layers inassociation with their colour and in reference to the known Cucompounds and associated corrosion products can assist specificsuggestions on their mineralogical composition [18–22]. For thegreen coloured areas where Cu is only detected, malachite (coppercarbonate) is the suggested corrosion compound, most commonlyfound in archeological copper alloys. In the green areas where Cuand Cl co-exist, atacamite, clinoatacamite, paratacamite or evennantokite might be present. For the later product one should keepin mind that the stratigraphic location of nantokite depends onmany factors including the degree of cleaning whether chemical ormechanical, loss of upper corroded layers either by poor mechani-cal integrity (physical loss) or intentionally, and the percentage ofchlorine present in the object and/or its vicinity. A typical strati-graphy of the bronze’s disease phenomenon assumes the presenceof nantokite near the metal alloy surface [22], however it can easilybe trapped inside other corrosion products. The nantokite is some-times colourless or whitish to greyish in colour but can be greenishdepending on impurities and accompanying minerals present.

The SEM-EDS analysis of nine (9) green coloured areas (Fig. 2b)showed minor amounts of S in four spots (0.5%–2%), in one spot(#346) 11.6%, whereas in the other four (4) spots the S contentwas found close to the detection limit. It is known that in Cubased alloys (especially in the outdoor Cu based monuments) twoCu-S contained compounds can be formed containing a S contentequal to 7.09% (brochantite, Cu4(OH)6SO4) and 9.04% (antlerite,Cu3(OH)4SO4), respectively. On the other hand, the micro-XRFanalysis of the green coloured areas didn’t confirm the presence

of sulphur in any of the nine spots examined. It should be notedhere that the detection limit for the micro-XRF analysis of S incopper-based compounds is estimated to be at least 0.15% or evenless. The elevated amount of S detected in one sample by SEM-EDX

266 A. Arafat et al. / Journal of Cultural Heritage 14 (2013) 261–269

Table 2Summary of qualitative results after analysis with the three techniques used: Scanning Electron Microscopy - Energy Dispersive X-Ray Spectrometer (SEM-EDS), portablemicro-XRF and portable LIBS.

Inventory no. - artefact Visualappearance

Analytical results

SEM-EDS* Portable �-XRF Portable LIBS Suggested compounds

(1) – 307Metallic jug with handleand long neck(Umayyad period)

Base metal Cu(ma), Sn(ma), Pb(ma),Zn(mi), Fe(mi)

Cu(ma), Sn(ma), Pb(ma),Fe(tr)

Cu(ma), Sn(ma),Pb(ma), Zn(mi)

Leaded bronze

Red n/a n/a Cu(ma), Pb(ma) Cu and Pb oxidesGreenish Cu(ma), Cl(ma), S(ma),

Fe(mi), Zn(mi), Sn(mi),Pb(mi)

n/a Cu(ma) Cu-S, Cu-Cl basedcompound(s)

(2) – 346Metallic jug(Umayyad period)

Base metal Cu(ma), Sn(ma), Pb(ma),Fe(mi), Zn(mi)

Cu(ma), Sn(ma), As(mi),Pb(ma)

Cu-Pb-Sn alloy,analysis performedat a point with ascratch

Leaded bronze

Red n/a Cu(ma), Cl(ma), Pb(ma),Sn(mi)

Cu(ma), Pb(ma) Cu - Cl compound(s), Pbcompounds and possiblyCu oxides.

Greenish Cu(ma), Sn(ma), Pb(ma),S(ma), Cl(ma), Fe(mi),Zn(mi)

Cu(ma), Cl(ma), Pb(ma),Sn(tr)

Cu(ma) Cu-S, Cu-Cl, and Pb basedcompound(s)

Brown n/a Cu(ma), Sn(ma), Cl(mi),As(mi), Pb(mi)

n/a Cu based oxide(s), Sncompound (possiblycassiterite), minor amountof Cu - Cl compound(s)

(3) – 347Metallic jug(Umayyad period)

Base metal Cu(ma), Sn(mi) n/a Cu-Pb-Sn based Copper alloy

Greenish Cu(ma), Cl(ma), S(mi),Fe(mi), Zn(mi), Sn(mi),Pb(mi)

n/a Cu - Cl compound(s)

(4) – 208Copper-base engravedbracelet(Start of Ottoman periodand end of Mamlokiperiod)

Base metal Cu(ma), Zn(ma), Fe(mi)Sn(mi), Pb(mi)

Cu(ma), Zn(ma), Pb(mi),Sn(mi-tr), Fe(tr), As(tr)

Cu-Pb-Zn-based Leaded brass

Red n/a Cu(ma), Zn(ma), Pb(mi),Sn(mi-tr), As(tr)

Cu(ma), Zn(mi) Copper oxide(s)

Greenish Cu(ma), Zn(mi), S(mi),Cl(mi), Fe(mi), Sn(mi),Pb(mi)

Cu(ma), Zn(ma), Cl(ma),Pb(mi), Sn(mi-tr)

Cu based Cu - Cl compound(s), Zndepletion

(5) – 216Copper-base roundedsection bracelet(Ottoman period)

Base metal Cu(ma), Zn(ma), Fe(mi) Cu(ma), Zn(ma), Pb(mi),As(tr), Fe(mi), Ni(mi)

Cu(ma), Zn(ma) Brass

Red n/a Cu(ma), Cl(mi), Ca(mi),Fe(tr), Pb(tr), As(tr)

n/a Major amount of Cuoxide(s). Minor amounts ofCu - Cl compound(s).Complete Zn depletionfrom the surface layer

Greenish Cu(ma), Cl(ma), S(mi), Fe(mi), Zn(mi), Sn(mi),Pb(mi)

Cu(ma), Cl(ma), Zn(mi),Fe(tr), Pb(tr), As(tr)

Cu based Cu - Cl compounds.Complete Zn depletionfrom the surface layer

Brown n/a Cu(ma), Zn(ma), Cl(mi),Ca(tr), Fe(tr), Pb(tr),As(tr)

n/a Cu, Zn oxides. Cu - Clcompound(s) in very minoramounts

(6) – 210Copper-base twistedbracelet(Ottoman period)

Base metal Cu(ma), Zn(ma), Fe(mi),Sn(mi), Pb(mi)

n/a Cu-Zn-Pb based Brass with minor Pbcontent

Black Cu(ma), Zn(ma), S(mi),Cl(mi), Fe(mi), Sn(mi),Pb(mi)

n/a Cu and Zn-based Cu, Zn oxides. Minoramount of Cl basedcompound(s)

A. Arafat et al. / Journal of Cultural Heritage 14 (2013) 261–269 267

Table 2 (Continued)

Inventory no. - artefact Visualappearance

Analytical results

SEM-EDS* Portable �-XRF Portable LIBS Suggested compounds

(7) – 317Copper-base thin sectionBracelet(Ottoman period)

Base metal Cu(ma), Zn(ma), Fe(mi),Sn(mi), Pb(mi)

Cu (ma), Zn(ma), Pb(mi),Sn(mi), Ca(tr), Fe(tr)

n/a Leaded brass

Greenish Cu(ma), Fe (mi), Zn(mi),Pb(mi), Sn(mi), Cl(mi),S(mi)

Cu(ma), Zn(mi), Ca(ma),Pb(mi), Fe(tr), Sn(tr)

n/a Major amount of Cucompound (possiblymalachite), Ca compound,Zn depletion from thesurface

Brown n/a Cu(ma), Zn(ma), Pb(mi),Sn(mi), Fe(mi)

n/a Cu oxide with Sn surfaceenrichment (probablycassiterite), Zn depletionfrom the surface

White n/a Cu(ma), Zn(ma), Pb(mi),Ca(mi), Fe(mi), Sn(tr)

n/a Strong presence of Ca(possibly as calciumcarbonate) and soilcontamination

(8) – 320Copper-base engravedbracelet(Ottoman period)

Base metal Cu(ma), Zn(ma), Fe(mi),Sn(mi), Pb(mi)

Cu(ma), Zn(ma), Pb(tr),Fe(tr)

Cu-Zn-based Brass

Greenish Cu(ma), Cl(ma), S(mi),Fe(mi), Zn(mi), Pb(mi)

Cu(ma), Cl(ma), Zn(tr),Pb(tr)

Cu based Strong presence of Cu - Clcompound(s) and completeZn depletion from thesurface layer

Brown n/a Cu(ma), Zn(ma), Cl(mi),Ca(mi), Fe(mi)

n/a Cu, Zn-based oxides andminor amount of Cu - Clcompound(s)

White n/a n/a Zn-based Zn-based compound

(9) – 327Copper-base heart(Ottoman period)

Base metal Cu(ma), Zn(ma), Fe(mi),Sn(mi)

Cu(ma), Zn(ma) Cu-Zn-based, Sn(tr)on the backside,Zn(mi) on the frontside.

Brass

Red Cu(ma), Zn(ma), S(mi),Cl(mi), Fe(mi)

Cu(ma), Zn(ma), Ca(mi) n/a Cu oxides. Cu presents asurface enrichmentrelatively to Zn

Soldering n/a Cu(ma), Zn(ma), Pb(ma),Sn(ma)

Cu (ma), Pb(ma),Sn(ma)

Solder compound based onSn and Pb

Yellow n/a Cu(ma), Zn(ma), Ca(mi) na Cu and Zn oxides

(10) – 323Copper-base ringOttoman period till endof World war (I)

Base metal Cu(ma), Zn(ma), Sn(ma),Pb(mi), Fe(mi)

Cu(ma), Zn(ma), Sn(ma),Pb(mi), Fe(tr)

n/a Gunmetal

Greenish Cu(ma), Zn(ma), Sn(ma),Cl(ma), S(mi), Fe(mi)

Cu(ma), Cl(ma), Sn(ma),Zn(mi), Fe(mi), As(tr),Pb(tr)

n/a Cu - Cl compound(s) withSn surface enrichment. Zndepletion of from thesurface

Black n/a n/a Cu(ma), Zn(ma),Sn(ma), Pb(mi)

Possible presence of Snoxide

White n/a Cu(ma), Zn(ma), Ca (ma),Sn(ma), Fe(mi), Pb(tr)

Ca based compoundunderneath which is a Cubased compound

m ents aa of Al

amowtddsocct

a: major; mi: minor; tr: trace refer to a semi-quantitative assessment of the elemt this spot for the particular technique). In the SEM-EDS analysis variable amounts

nalysis and its absence from the respective micro-XRF spectrumight be partly explained due to the peak deconvolution problem

f the SEM-EDX analyser, due to the significant interference of S-Kith the strong Pb-M peak appeared in this particular case. For

he other four spots where S was detected in minor amounts, theifference observed with the micro-XRF results can be explainedue to the non-invasive character of the micro-XRF investigationince in the latter case the surface is analysed as it is; in the case

f the SEM-EDX analysis a powder sample is extracted from theorrosion layer thus representing better its bulk composition. Inonclusion and based on the SEM-EDX results, the presence of thewo Cu-S associated green corrosion products, brochantite and

bundance, whereas the abbreviation n/a indicates that no analysis was performedand Si were detected at all the corroded areas due to soil contamination.

antlerite cannot be excluded in four of the samples, however theiroverall contribution in the corrosion layer should be rather minor.

For the red-corroded areas, cuprite is most likely to be the redproduct though when lead is present, minium (lead oxide) cannotbe excluded before further mineral analysis is carried out. Othercorrosion products were present in different colours: brown, grey,black and white layers. The brown corrosion layers show in manyoccasions the co-existence of Cu, Sn, Zn and Pb. It seems that Zn

is depleted from the surface, while cassiterite (SnO2), ZnO andPbxOy are found concurrently with tenorite (CuO) and/or cuprite(Cu2O). White corrosion layer as in 317, 320 and 323 are Zn-basedthough calcium is present in the layer probably originating from the

268 A. Arafat et al. / Journal of Cultural

Fig. 3. Examples of micro-XRF (a–c) and Laser-Induced Breakdown Spectroscopy(LIBS) (d–f) spectra for the object 346 (#2) obtained for the base metal, green andred-corroded areas; a: base metal (filtered micro-XRF excitation); b: green area(unfiltered micro-XRF excitation); c: red area (unfiltered micro-XRF excitation); d:base metal (LIBS); e: green area (LIBS); f: red area (LIBS).

Heritage 14 (2013) 261–269

soil contamination. The black layer shows quaternary metal oxidecomposition Cu-Sn-Pb-Zn in the objects 327 and 323. The grey cor-rosion layer detected in the object 323 shows only Cl, which mayrather refer to nantokite or halite from the burial soil deposition. Asoldering material was analysed in the Umayyad jug (347) and theOttoman heart-like object (327) and in both cases it is based on aCu-Sn-Pb solder.

4.4. Technical aspects

The micro-scale heterogeneity of metal alloys affects criticallythe precision of the results generated by microanalytical techniques(i.e. when the spot size analysed is at the scale of 0.1–0.2 mm orless). In a previous study [7] it has been shown that even for amodern certified copper quaternary alloy the standard deviation ofsingle spot micro-XRF measurements could be up to 10% for Cu, 20%for Zn, 20% for Sn and 75% Pb [7]. However, the variation of meanvalues deduced from greater than 1 mm2 area scan measurementsis only few percent. It is thus recommended that mm size probescan compensate local inhomogeneities and offer more representa-tive results of the base metal composition. In conclusion, a singlespot micro-XRF measurement on a copper quaternary alloy mightinclude a 5-15% uncertainty due to heterogeneity for Cu, Zn andSn and much higher for Pb. These uncertainties are indicative andrepresent rather the optimum scenario for the micro-XRF analyseson the Islamic Cu based artifacts.

The micro-XRF and SEM-EDS analyses are compared using theCorrelation Factor (R2). This is done considering the critical ele-ments in the Cu-alloyed artefacts, i.e. Pb, Sn and Zn. The results(R2 = 0.9837, 0.9976 and 0.7338 for Sn, Zn and Pb, respectively)reflect mostly the degree of heterogeneity of the alloyed elementsshowing a rather large heterogeneity for the Pb. Comparing forexample the base metal analyses performed by means of SEM-EDSand micro-XRF analysis on the Umayyad jars and jug (no. 307, 346),remarkable differences in lead-to-tin ratios (Pb/Sn) are observed.Due to the alloys inherent heterogeneity, mostly in the Pb spatialdistribution, single micro-spot or small area analyses by both tech-niques do not ensure representative results of the base metal andthus the results obtained can be considered as semi-quantitative.

A recent study addressed the inter-laboratory comparability andreproducibility in quantitative XRF analysis of historic copper alloysby analyzing the same polished area of eight historical alloys andfour modern certified reference materials [24]. The results showedthat the overall inter-laboratory reproducibility is greater than50% for all elements (except Cu, Zn, and Sn) including Fe, Ni, As,Sb and Pb. One of the main conclusions of this study is that thewider adoption of quantification methods utilizing the Fundamen-tal Parameters method with standards will offer the possibility ofsignificant improvement in the inter-laboratory reproducibility.

Comparing the SEM-EDS with the in situ application of themicro-XRF and LIBS techniques, it is clear that due to their porta-bility a large number of analyses per artefact can be conductedand this compensates to a great extent their analytical limitationsand restrictions in the diagnostic characterization of the alloys basemetal and associated corrosion products.

5. Conclusions

The in situ application of micro-XRF/LIBS techniques combinedwith the SEM-EDS analysis of Islamic copper alloyed artefacts from

the collection of the Umm Qais museum allowed for a compo-sitional based categorisation of the studied artefacts and revealassociations according to date and function. Umayyad jars con-sist of leaded bronze, Ottoman bracelets are made of brass and

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A. Arafat et al. / Journal of Cu

eaded brass, while the late Ottoman ring composition correspondso leaded gunmetal.

Despite the compositional differences, the type of corrosionroducts detected on the surface found to be similar among thetudied artefacts. Green, red and brown coloured corrosion pro-ucts are the ones most commonly observed. Since the elementalnalyses performed cannot provide unambiguous identification ofhe corrosion products, further mineralogical analysis of the crys-alline compounds (X-Ray Diffraction “XRD” analysis) is required.

The similarities observed among the corrosion products of cop-er artefacts with different composition are likely to be due tombient environmental conditions rather than internal inherentorrosion susceptibility of the alloy. The seasonal environmentalonitoring for one year (September 2006–August 2007) at theuseum gallery shows the influence of humidity and tempera-

ure with season, nevertheless they remain within the acceptableanges. Gaseous pollutants were also monitored and TVOC seem toe at relatively worrying levels, especially with their unidentifiedource and daily levels. Further investigation into their sources andotential reduction within the museum gallery sounds necessary.nother recommendation would be measuring surface tempe-ature and relative humidity at the metal surface together withnternal and external ambient parallels. Such measurement canelp calculating Dew Point Temperature, the temperature at whichondensation occurs on a metal surface, therefore indicating poten-ial risk by hydrolysis and carbonation of copper alloyed artefacts.he scope for comprehensive and targeted environmental moni-oring study is still standing in the view of available technicalevelopments and lack of the needed environmental assessment

n Jordanian museums. Since the conditions of the objects are badnd the display environmental conditions are uncontrolled, thehoices left for the conservators are to stabilise the condition byither immediate treatment of the artefacts or preventive conser-ation such as creating a local microclimate imitating the burialnvironment, if possible. A recommendation can be using an oxy-en scavenger and a heat seal with a humidity level monitor (e.g.SCAL), which would keep suitable microclimate for 3–5 years.

The use of portable analytical techniques is very helpful fornalysing cultural heritage materials and for monitoring their dete-ioration or treatment. However, meaningful monitoring requireseriodical (seasonal) measurements, which imply accessibility tortefacts, availability of qualified personnel, financial resources andime. All these factors need thorough preparation and considerationefore and during a monitoring campaign.

cknowledgement

This work has been supported in part by the European Com-ission, Project PROMET (Contract: FP6-2002-INCO-MPC-1). The

uthors are very grateful to the scientists of Metallographic andorrosion Laboratories at the Royal Scientific Society, the Depart-ent of Antiquities of Jordan and curators at Umm Qais museum

nd the Jordanian Numismatic Museum at Yarmouk University,rbid, Jordan.

ppendix A. Supplementary data

Supplementary data associated with this article can beound, in the online version, at http://dx.doi.org/10.1016/j.culher.012.07.003.

Heritage 14 (2013) 261–269 269

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