decorated archaic pottery from the heracles sanctuary at thebes

19 Pages·2013·2.22 MB·English

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Archaeometry55,5(2013)806–824 doi:10.1111/j.1475-4754.2012.00705.x
DECORATED ARCHAIC POTTERY FROM THE HERACLES
SANCTUARY AT THEBES: A MATERIALS, TECHNOLOGY AND
PROVENANCE STUDY*
G.MASTROTHEODOROS,1,2K.G.BELTSIOS,1†N.ZACHARIAS,3V.ARAVANTINOS4
andK.KALLIGA4
1DepartmentofMaterialsScienceandEngineering,UniversityofIoannina,45110,Ioannina,Greece
2LaboratoryofArchaeometry,InstituteofMaterialsScience,NCSRDemokritos,15310Ag.Paraskevi,Attiki,Greece
3LaboratoryofArchaeometry,DepartmentofHistory,ArchaeologyandCulturalResourcesManagement,
UniversityofPeloponnese,24100OldCamp,Kalamata,Greece
49thEphorateofPrehistoricandClassicalAntiquities,MinistryofCultureandTourism,MuseumofThebes,
22120Thebes,Greece
Forty-sevendecoratedsamplesofArchaicpotteryexcavatedataHeraclessanctuary(Thebes,
Boeotia)werestudiedthroughacombinedsurfaceandbodyapproach,usingnon-destructive
techniques.MostofthesampleswerearchaeologicallyclassifiedasTheban/Boeotian,others
asCorinthianandafewaspossiblyEuboean.Thetechniquesemployedwereopticalmicros-
copy and SEM–EDAX (micromorphology and compositional analysis of the surfaces) and
XRF for the analysis of the ceramic body. The results provided information on the techno-
logical level of the collected pottery as well as on the relation of the chemistry and micro-
morphologyofthepigments,aimedatassistingprovenancestudies.
KEYWORDS:ARCHAICPOTTERY,PIGMENTS,PROVENANCE,SLIP,THEBES,XRF,
SEM–EDAX
INTRODUCTION
Macroscopic examination of pottery, with an emphasis placed upon surface features, served
archaeology well for a substantial part of the 20th century and continues to be used alone as a
source of valuable conclusions; archaeologists usually examine surface decoration in order to
assessissuessuchasproduction/technologycapacityandtrends,evolutionofsites,provenance
andtradepatterns.Elaborateversionsoftheapproachhaveledtoimpressiveresults;forexample,
Boardman has relied substantially on his decorated Greek pottery expertise amassed from
macroscopic studies for his key work on Greek colonization (Boardman 1999). Microscopic
examinationofpotterymakesuseofphysicsandchemistrymethodsappropriateforthechemical
and microstructural study of materials, and eventually attempts to address almost the same
questions as macroscopic examination, preferably in a complementary manner. For the micro-
scopicapproach,tinyfragmentscanturnouttobeatleastasusefulassizablefragmentsorintact
objects;forexample,atinypotteryfragmentproperlyorientedinaSEM–EDSholderconstitutes
across-sectionmadeavailablenon-destructivelyandcanbestudiedwithregardtocomposition,
layeringandsoon.
Inthesouth-eastBalkansandtheAegean,decorationtechniqueshavebeenappliedsincethe
verybeginningofpotteryproduction,mainlyintheformofengravedandsimplycolouredmotifs.
*Received30November2011;accepted5June2012
†Correspondingauthor:[email protected]
©2012UniversityofOxford
DecoratedarchaicpotteryfromtheHeraclessanctuaryatThebes 807
The engraved motifs were in most cases produced prior to firing, while a variety of coloured
earths (usually calcium- or magnesium-rich clays for white colouring, iron-rich clays for red
colouringetc.)werealsoappliedtothesurface.Followingfiring,thevaseswerefurtherdecorated
usingnaturalpigments,possiblycombinedwithorganicadhesives.
As early as the fifth millennium bc, an elaborate technique that led to permanent results
evolved.Theso-called‘ironreductiontechnique’(IRT)allowedancientpotterssimultaneouslyto
developredandblackmotifsusingasinglefiring(Nolletal.1975).TheIRtechniqueprovedto
be extremely effective and continued to be used for thousands of years; pottery of the archaic
period,aswellasthewell-knownhigh-qualityAtticglosspotteryofclassictimes,wasproduced
using this method (Noble 1960; Hofmann 1962; Tite etal. 1982;Aloupi 1993; Maniatis etal.
1993).
According to the IRT, a high-iron and low-calcium, usually illitic, clay is selected and then
subjected to extensive elutriation, leading to a fine final product (to be applied for decoration
purposes)exhibitinganincreasedAlO/SiO ratioandanenhancedironcontent.
2 3 2
Thefiringbeginsinanoxidizingatmosphere,whichisretaineduntilthetemperatureapproxi-
matesthe800–850°Crange;atthispointthefurnaceatmosphereischangedtoareducingone,
possibly by introducing wet or resin-rich fuel and by sealing the air pipes. The CO and HO
2
generated by the fuel act as reducing agents, and thus the iron present in the clay is converted
from Fe(III) (hematite contained in the clay) to Fe(II). Black spinels such as magnetite
(Fe2+Fe3+O),hercynite(FeAlO,)and,atrelativelyhightemperatures,wustite(FeO)areformed
2 4 2 4
(Titeetal.1982;Tangetal.2001).Asaresult,theclaydevelopsadark-blackcolour.Atthesame
time,thedecorationlayersintersandvitrifies;thelatteralterationispromotedbythepresenceof
alkali ions that act as flux (mainly potassium in illitic clays); in addition, the smaller the clay
particlesize,theeasierthesinteringbecomes(Hofmann1962;Nolletal.1975;Titeetal.1982;
Ingoetal.2000;Mirtietal.2006).
Atthefinalstageofthefiring,theatmosphereischangedbackintoanoxidizingone,whilethe
temperaturebeginstofallbelow850°C.Thusallexposedpartsoftheobject(includingthebody
of the object) reoxidize readily and gain light-red hues (the exact colour depends on the clay
composition),whilethevitrifieddecorationlayerisunabletoreoxidizeandthusretainsitsblack
colour.
Forwhitedecoration,claysrichincalciumor/andmagnesiumwerewidelyinuse(Swannetal.
2000;Ferrenceetal.2002),whilekaolinwasanaccessiblealternativeandwasroutinelyencoun-
teredinthedecorationofwhitelekythoiduringtheclassicalperiod(Nolletal.1975).Inaddition,
redhuescouldbesimplyachievedbytheuseofferruginousclayforthebody,inwhichcasethe
non-covered(bythedecorativeclay-black)areasservedasredpatterns;ironochreswerealsoin
useforthesamepurpose(Nolletal.1975).Further,itwaspossibleforadifferentgradeofthe
rawmaterialusedfortheblackdecorationtoserveasasourceofafinalredcolour:thepotters
simplyhadtocollectaportionduringtheelutriationandbeforeitscompletion.Thisquantity,less
refined and thus coarser, would create a layer with a structure that was more open and less
susceptible to complete vitrification during the reduction step; consequently, the latter layer
wouldbeabletoturnredduringthereoxidationstep.
Purple is a colour encountered less frequently in the decoration of pottery. It has been
proposedthatthiscolourcouldbeachievedbymixingironochreandaportionofrefined(used
for the black motifs) clay (Noble 1960; Mirti etal. 2006). The unusual purple colour might
then result from the incomplete reoxidation of the iron particles (at the final oxidative stage of
the firing), leading to the coexistence of a certain appropriate balance of Fe(II) and Fe(III)
(Mirti etal. 2006).
©2012UniversityofOxford,Archaeometry55,5(2013)806–824
808 G.Mastrotheodorosetal.
Theassemblageconsideredinthisworkwasrecoveredfromasmallexcavationplotofabout
350m2nearafamousThebantemenos,thetempleofIsmenianApollointhecentreofThebes,
centralGreece.AncientThebesisusuallymentionedasthebirthplaceoftheheroHeracles.The
excavation resulted in the collection of hundreds of artefacts, which clearly indicates that an
ancientsanctuarydedicatedtoHeracleswaslocatedatthissite(Aravantinos2009).Thecorecult
area was an open-air monumental eschara (ash altar), measuring at least 9 ¥ (9–10) m2 (the
structurecontinuestotheeast,beneaththemodernroad).Itwascarefullybuiltofstonesneatly
squared on their outer faces. Courses of small bricks and quantities of small fieldstones on the
insideofthestructureperhapsindicateattemptstodemarcatethelayersofashwithapyramid-
shapedconstruction.
Thealtarwasfoundtobefullofpottery,ash,animalbones,metalobjects,sculpturalvasesand
evensomefaience,andwasusedprobablyfromtheLateGeometricII(lateeighthcenturybc)to
the EarlyArchaic period (seventh century bc).The vast bulk of the votive offerings consists of
painted wheel-made pottery (drinking, mixing and serving vases, cosmetics containers and
lamps)andunpaintedhand-shapedpottery(kettles)(Aravantinos2010).Thelocalpotteryhasan
eclectic character, depending on the neighbouring schools (Attic, Protocorinthian and Euboeo-
Cycladic).ThefiguredscenesaresecondonlytothoseofAtticainthevarietyoftheirrepertoire,
including hunting, dancing and mythological scenes, and so on. A peculiar local group (‘bird
cups’; upper part of Fig.1) is decorated with painted birds and, later, with linear motifs. The
presenceofProto-Corinthianpotteryisverystrongintheashaltar(Fig.1,bottomright),along
with vases of the ‘Thapsos’type. Probably because of the increasing height of the offerings, at
some point after the middle of the seventh century it became necessary to seal the site and
Figure1 Upperleftandright:twoTheban,‘birdcup’samples.Bottomleft:characteristic,homogeneous‘high-quality’
blackslip(‘Boeotian’sample).Bottomright:arepresentativeCorinthiansamplewithblackandpurple-colouredmotifs.
©2012UniversityofOxford,Archaeometry55,5(2013)806–824
DecoratedarchaicpotteryfromtheHeraclessanctuaryatThebes 809
relocate the ritual centre a few metres north. The significance of this discovery is further
underlinedbythefactthatPindar(15th.66–77)andPausaniasinhisBoeotika(Paus.IX,11,1–7)
describesuchasanctuaryindetail.
Fromthevastnumberofpotteryfragments,47wereselectedforthepresentstudytoprovide
arepresentativepictureofthepotteryfindingsandbyfollowingtypologyanddecoration.Most
ofthefragmentsbelongtotheEarlyArchaictoArchaic(seventhtosixthcenturiesbc),theperiod
duringwhichthesanctuarywasinfullactivity.
More specifically, the selection included only decorated samples that, according to the
archaeological classification, were assigned as ‘local Theban’, ‘Corinthian’ and ‘possibly
Euboean’,andonesamplecharacterizedas‘possiblyAttic’.
Thescopeofthestudymaybesummarizedasfollows:
(1) Anexperimentalinvestigationofthetechniquesandpigmentsusedforthedecorations.
(2) Apossibleconnectionbetweenthetechnologicalfeaturesofthedecorativepigmentsandthe
provenanceofthesamples.
(3) Acomparisonoflocallyproducedwithother,contemporary,products.
EXPERIMENTAL
The samples were subjected to examination in the as-received state, although all samples had
been cleaned in the conservation laboratory of Thebes Museum. The methods used in the
examinationareasfollows:
(a) Opticalmicroscopy(OM):priortofurtherinvestigation,thesampleswereobservedundera
Zeiss (47 50 22-9022) stereoscope at 1¥ to 4¥ magnifications. Thus proper selection of the
samplesforfurtherexaminationbymeansofelectronmicroscopywasachieved.
(b) Scanning electron microscopy combined with energy-dispersive X-ray analysis (SEM–
EDAX):aFEISEM–EDAXwasused(modelInspect,withaSuperUltraThinWindow)forthe
micromorphological and quantitative investigations. The samples were observed alternately in
thesecondary(SE)andbackscattered(BSE)electronmodes.Thevoltageappliedonthefilament
was25kVandeveryspectrumwascollectedfor150liveseconds(totalcountsª50000).
(c) X-ray fluorescence (XRF): a milli-XRF unit with a Rh target and a Si-Pin detector (XR-
100CR, Amptek Inc.), described at length elsewhere (Zacharias etal. 2009), was employed.
Everysampleunderwenttwosetsofmeasurements,thefirstat15kVand100mAformajorand
minorelementsandthesecondat40kVand300mAforthetraceelements.Eachspectrumwas
collectedfor1000satarelativelystablecountingraterangingbetween370and480cps.
(d) X-ray diffraction (XRD): for identification of the crystal structure of specific pigments, a
Siemens XRD 500 diffractometer with a Cu–K anticathode was used.The voltage was 40kV
a
andthecurrent35mA,whileallthediffractionspectrawerecollectedintherangebetween2and
85°(2q)withastepof0.04°/2s.
RESULTSAND DISCUSSION
Blackdecoration
The observation of the dark-brown to black-coloured decorations revealed that the samples are
highly differentiated in terms of their colour/texture, micromorphology and chemical composi-
tion.At the same time, it is obvious from the microstructure and chemical composition of all
samplesthatversionsoftheIRTmethodswereemployedinallcases.Withregardtocomposition,
©2012UniversityofOxford,Archaeometry55,5(2013)806–824
810 G.Mastrotheodorosetal.
therelevantfingerprintsareasfollows:moderatetohighAlO/SiO ratio,highironcontent,low
2 3 2
Ca and Mg content, and a strong presence of alkalis (K and Na). A characteristic plot of the
AlO/SiO ratio and the total alkaline earth content of the pigments compared with the body
2 3 2
clays is presented in Figure2. The considerable differences are an indication that in most
specimens a distinct raw material, selected especially for this purpose, has been used as a
pigment.
TheCaOcontentversusAlO/SiO theratioofthepigmentsispresentedinFigure3.Inorder
2 3 2
to compare the samples under investigation with previously published data, five samples dis-
cussed in another paper have been introduced in the chart (indicated by crosses in Fig.3; data
from Maniatis etal. 1993). These five samples are classical Attic and are regarded as high-
quality. On the right-hand side of the chart appear the ‘high-quality’samples (highAlO/SiO
2 3 2
ratio and low CaO content, similar to the Attic ones), while the ‘low-quality’ samples (less
elaboraterawmaterialselectionandprocessing)areshownontheleft.Yet,atleastonthebasis
of the compositional parameters employed in Figure3, one might assume that samples of
intermediatequalityexistaswell.
Onthebasisofmicroscopicexamination,allspecimensunderinvestigationpresentthesame
generalmicromorphology,characterizedbyasinteredlayerattachedtotheporousclaybody;this
is largely a reflection of the employment of IRT decoration approaches. Microscopic differen-
tiation of the various samples under consideration is possible on the basis of the thickness and
texture of the sintered layer. More specifically, although some samples present a well-vitrified
uniformlayer,inmanyothersthislayerisnotonlyunevenbutalsospottedwithopen(bloating)
pores(Fig.4).
ThesecharacteristicporesarecausedbythepresenceofcarbonatessuchasCaCO andMgCO
3 3
(whichdecomposewithCO evolution)andalsobythestrongreductiveconditions,whichlead
2
Figure2 TheMgO+CaOcontentversustheAlO/SiO ratio:rectanglesrepresentbodyclay,andtrianglesrepresent
2 3 2
blackpigments.
©2012UniversityofOxford,Archaeometry55,5(2013)806–824
DecoratedarchaicpotteryfromtheHeraclessanctuaryatThebes 811
Figure3 The CaO content versus the AlO/SiO ratio for the dark-brown to black pigments. Circles indicate the
2 3 2
samplesunderconsideration,whiletheplussigns(‘+’)indicatefivesamplesfromManiatisetal.(1993).
Figure4 Left: a black layer with bloating pores (backscattered electron detector, 5000¥). Right: a well-vitrified,
homogeneousblacklayer(secondaryelectrondetector,8200¥).
totheremovalofoxygenfromtheFe(III)oxides(FeO →2FeO+0.5O)oftheappliedlayer.
2 3 2
Theevolvedgasespenetratethequasi-meltedmassofthepigmentsandleaveimprintsintheform
of characteristic pores. As the latter pores affect the surface morphology and thus the optical
properties of the pigments (reduction of glossiness etc.), they are regarded as defects and their
detectionisanindicationofanunsuccessfulprocess(intermsoftherawmaterialselection,the
©2012UniversityofOxford,Archaeometry55,5(2013)806–824
812 G.Mastrotheodorosetal.
treatmentand/orfiringconditions,andthedurationandextentofthereducingstage).Moreover,
it is well known that such pores are absent in high-quality samples (Tite etal. 1982; Maniatis
etal.1993;Mirtietal.1996,2006).
Consequently, it was noticed that the ‘high-quality’ (in terms of composition) samples
appeared to be homogenous in terms of micromorphology and usually they do not exhibit
bloating pores – or only exhibit them to a limited extent. With regard to the archaeologically
estimatedprovenanceofsamples,itisnotedthatallthe‘Corinthian’samplesareincludedinthe
high-qualitygroup.Ontheotherhand,althoughthemostofthe‘Theban’samplesappearedtofall
into the low-quality group, some of them present high-quality characteristics (highAlO/SiO,
2 3 2
low CaO and a well-vitrified, homogeneous microstructure). Two characteristic examples are
presentedinFigure1:theupperleftsampleexhibitslowqualityanddullblackdecoration,while
thebottomleftsamplehasbeendecoratedwithahigh-quality,shinyblackpigment.
Reddecoration
By visual examination, red decorations on the samples could be divided into two groups: the
samplesofthefirstgroupbearcolouredareasthatappeardullandhavearoughsurface,whilein
thesamplesofthesecondgroupthecolouredareasexhibitacharacteristicglossysurface.This
separationintotwogroupsisalsoevidentintermsofcomposition.InFigure5,wheretheFeO
2 3
content versus the AlO/SiO ratio of the red pigments is presented, two distinct groups are
2 3 2
present;thefirstappearsontheright-handsideofthechartandischaracterizedbyanAlO/SiO
2 3 2
ratiobelow0.4andanFeO contentabove15%,whilethesecondexhibitsanAlO/SiO ratio
2 3 2 3 2
above0.5andanFeO contentbelow15%.
2 3
The fact that the compositionally differentiated pigments were also micromorphologically
distinctwasnotsurprising.Thehigh-FeO/low-AlO/SiO grouppresentsamoreorlessopen
2 3 2 3 2
Figure5 TheFeO contentversusAlO/SiO ratioofthereddecorativepigments(wt%oxides).
2 3 2 3 2
©2012UniversityofOxford,Archaeometry55,5(2013)806–824
DecoratedarchaicpotteryfromtheHeraclessanctuaryatThebes 813
Figure6 Twomorphologicallydifferentiatedsamples:ontheleft,arough,grainy,non-vitrifiedlayerofredpigment
(secondaryelectrondetector,350¥);andontheright,aquasi-vitrifiedsamplesimilarto,thoughlessvitrifiedthan,that
oftheblackpigments(backscatteredelectrondetector,7000¥).
structure(Fig.6),whilethehigh-AlO/SiO samplesaresimilartothewell-vitrifiedblacklayers
2 3 2
(Fig.7). It must be also noted that in all the red-decorated samples, red pigments have been
appliedtothesurfacepriortofiring.Thisisevidentfromthemicromorphologicalfeaturesofthe
pigments,whichinallcasesexhibitamoreorlessvitrifiedstructure.
In view of the overall composition and known decoration practices for pottery of the type
considered herein, red pigments with an iron content exceeding 25% (w/w FeO) can be
2 3
classified as iron ochres that have been applied on the surface. This is the case for 4 out of 11
samples:allofthemalsopresentthecharacteristicgrainy,openstructureoffiredochres(Fig.6,
left),whichiseasilydifferentiatedfromburntclays(Nolletal.1975).
Thetwopigmentswitharelativelyhighironcontent(15–20%)andalowAlO/SiO ratiomay
2 3 2
beidentifiedashigh-ironclays.Infact,theyaredifferentiatedfromfiredochresnotonlybytheir
iron content, but also by their structure: while the ochres are grainy, the high-iron clays under
considerationaremuchmoreevenandvitrifiedtoagreaterextent(Fig.6,right).However,both
of these pigments retain enough porosity, a fact that makes them ideal for IRTuse, as they are
easilyreoxidizedaftertheendofthereducingstageofthefiring,thuspermittingthesimultaneous
productionofredandblackshades.
Ontheotherhand,fourpigmentsformaseparate,thirdgroupwitharelativelylowironcontent
but a high AlO/SiO ratio. Their chemical characteristics are almost identical with those of
2 3 2
the black pigments. Furthermore, they present the characteristic, well-vitrified structure of the
high-qualityblackpigments(Fig.7).
Thesefoursamplescomefrompotsonwhichtherearenoblack-colouredmotifs.However,the
red-colouredpigmentsexhibitmorphologicalandchemicalcharacteristicsthatareidenticalwith
thoseofthetypical—fortheIRtechnique—blackpigments.Thusitcanbeconcludedthattheraw
materialsusedforthespecificredpigmentaresimilartothosecommonlyusedfortheproduction
of black motifs; however, the final colour is red because the pots had been fired in a single
oxidizingstep.
©2012UniversityofOxford,Archaeometry55,5(2013)806–824
814 G.Mastrotheodorosetal.
Figure7 Awell-vitrifiedredpigment(backscatteredelectrondetector,5000¥).
Inconclusion,thereddecorationshadbeencreatedbyusingthreedistinctrawmaterials:iron
ochres, iron-rich clays (which are open-structured and reoxidize readily) and finely processed
clay (identical, or at least very similar, to those used for black pigments) burned in a single
oxidizingstage.
Purpledecoration
Purple-coloured motifs are found on the surface of all the ‘Corinthian’(5) and two ‘Theban’
samples(Fig.1,bottomright).ItmustbenotedthatpurplewasusedfreelyonProto-Corinthian
andCorinthianvases(Payne1971).Fromamacroscopicpointofview,therewasnosignificant
differentiationamongthesevensampleswithregardtothehueofthecolour.Furthermore,allof
thesamplesexhibitsimilarroughandunevensurfacemicromorphology(Fig.8),buttheydiffer
considerably with regard to the thickness of the pigment layer (which varies between 5 and
25mm).
Observation of the pigment at a magnification above 10 000¥ revealed an unexpected
morphology; that is, particles with dimensions ranging between 0.3 and 1.2mm (Fig.8,
right).
©2012UniversityofOxford,Archaeometry55,5(2013)806–824
DecoratedarchaicpotteryfromtheHeraclessanctuaryatThebes 815
Figure8 Left:theroughsurfaceofthepurplepigment(backscatteredelectrondetector,390¥).Right:thegrainytexture
ofthepurplepigment(backscatteredelectrondetector,30000¥).
Withregardtochemicalcomposition,themaincharacteristicisthehighironcontent,whichin
all cases exceeds 30wt% FeO. Another characteristic is the relatively low AlO/SiO ratio
2 3 2 3 2
(0.30–0.37),whichindicatesthepresenceofcoarseclay.
On the other hand, spectra collected on areas with high concentrations of tiny particles
exhibitedanevenhigherironcontent,whichinsomeareasreached80%;thisfact,combinedwith
themorphologicalcharacteristics(seebelow),ledtotheconclusionthattheparticlesarepureiron
oxide. In order to identify the crystal structure of the iron particles, an XRD spectrum was
collected from the surface of a sample. XRD revealed that iron in the purple pigment is in the
formofhematite.
Theseironpigmentshadbeenappliedontothepotterysurfacepriortofiring,afactthatwas
made evident by micromorphological observations, which revealed that the pigment is sintered
(Fig.8, left and right). Also, in cases where purple had been applied over black pigment, a
diffusion zone has been created between the two layers by the diffusion of iron particles in the
blackgloss.
It has been stated elsewhere (Mirti etal. 2006) that this unusual colour may be attributed to
the alternation of oxidizing–reducing–oxidizing conditions during firing: during the reducing
stage, Fe(III) is converted to FeO oxide, which—due to partial sintering—may not be fully
reoxidized upon the final reoxidization stage. The combination of Fe(II) (black-coloured) and
Fe(III) (red) oxides leads to the purple colour (Mirti etal. 2006). However, the XRD exami-
nation in the present study showed that the iron in the purple pigment is in the FeO state.
2 3
Furthermore, previous publications give no explanation for this peculiar iron particle morphol-
ogy. An extended research approach on ancient iron pigments (Mastrotheodoros etal. 2010)
revealed that high-iron (>90%) raw materials present a colour shift from red to purple upon
firingatgraduallyrisingtemperatureinoxidizingconditions.Morespecifically,apurplecolour
may develop at a temperature of 900°C or higher, and the colour change observed is explained
by the gradual shift of the iron particle dimensions. The purple hue is achieved when the iron
particles exceed 0.4mm in diameter. Thus although it is possible that a purple tint can be
©2012UniversityofOxford,Archaeometry55,5(2013)806–824