An Odyssey Through Time at EMPA

ART AND CHEMICAL SCIENCES

Chimia 55 (2001) 931-937copy Schweizerische Chemische Gesellschaft

ISSN 0009-4293

931CHIMIA200155 No11

An Odyssey Through Time at EMPA

Marianne Senna Wim Devosa Walter Fasnachta Thomas Geigera Franltoise MichelaAxel Ritterb Giuseppino Fortunatob

Abstract For years EMPA has made many contributions to research on historical materials and theirmanufacture and conservation in archaeology restoration and the preservation of historical monuments areasthat are somewhat exotic for a materials testing and research institute This involves complex preferably non-destructive investigations on objects that are often very valuable by means of organic and inorganic analysismethods The emphasis is on investigations of paints and varnishes on paintings and metals such as goldsilver copper bronze and iron The analysis of various materials and the associated problems are illustratedby a range of examples

Keywords Archaeometallurgy Archaeometry Art conservationmiddot Artists pigments

1 Introduction

Archaeology belongs to the humanitieswhereas the restoration and conservationof cultural heritage also includes craftand scientific components In many are-as all three are now dependent upon sci-entific support in order to be able to con-duct research As a result archaeometryhas developed as a bridge between thesesubjects The questions raised are oftenbasic such as the determination of organ-ic and inorganic materials their state ofpreservation their conservation produc-tion and provenance It is sometimesalso a matter of determining an objectsauthenticity With a metal object for ex-ample interest is primarily in its formand thus function which are often hiddenunder corrosion and then in its produc-tion and processing and if possible itsprovenance so that quality features andthe age of the object may be ascertainedThe artistic impact of a work of art re-

mains only as long as it is physically in-tact All objects are subject to ageing ofone kind or another depending upon thematerial composition and environmentand upon handling or use If the ageing

Correspondence M SennaTel +41 1 8234343E-Mail mariannesennempachaSwiss Federal Laboratories for Materials Testingand Research (EMPA)Oberlandstr 129CH-8600 DGbendorfbEMPALerchenfeldstr 5CH-9014 St Gallen

process is to be understood it is essentialto carry out a careful examination ofthe individual factors such as climaticconditions pollutant content of air andsoil presence of microorganisms and ofcourse the material composition of theobject itself Once any interrelationshipshave been identified it is often enough tomake slight changes to these factors inorder to retard the ageing process How-ever if ageing has progressed so far thatthe continued existence of the object is inquestion conservation measures are alsorequiredReference is made to such findings

when selecting the materials used for car-rying out restoration Where appropriatetraditional materials are used Howeverthis is often impossible and modernproducts are used instead In this casethorough knowledge of the compositionof the products used and their chemicalphysical and biological characteristics isvital especially with regard to possibleinteractions with the original materialsinto which they are incorporatedState authorities together with univer-

sity departments the art trade and muse-ums thus depend upon being able to col-laborate with a research laboratory whichnot only has experience of characterisingand testing inorganic and organic materi-als and ofthe destructive influence of mi-croorganisms but is also able to carry outsuch complex investigations on a routinebasis EMPA has a long tradition of de-veloping exotic applications for material-testing methods and research resultsCombining the skills of scientific re-

searchers with comprehensive facilitiesand an efficient service infrastructureEMPA is in an ideal position to use itsknow-how to devise elegant solutions totricky problems

2 Organic Materials

Organic materials are often the sub-ject of restoration work but are of lesssignificance in relation to archaeologyand the conservation of cultural heritagebecause investigating such materials iscomplex and costly Moreover they havea shorter life than inorganic and metallicmaterials because they can be brokendown substantially faster by environmen-tal conditions such as heat moisturelight pollutants and microorganismsIn works of art on the other hand or-

ganic materials such as wood paper andtextiles play an important part becausethey are generally protected from weath-ering and may consequently often be pre-served for centuries Considerable timeand money are devoted to restoring andconserving works of artWhich analytical methods are suitable

for investigating works of art thus mak-ing it possible to answer complex ques-tions Over the last decade various tech-niques have been refined and combinedin such a way that powerful analyses canbe carried out non-destructively or usingonly very small samples However triedand trusted techniques such as opticalmicroscopy still provide valuable assist-ance


Two examples from the ChemistrySection of EMPA St Gallen illustratethis point When restoring furniture thequestion always arises of the identity ofthe materials that the craftsman used toproduce the piece The first question is toidentify the species of wood which de-fines the strength structure and colour ofthe furniture The restorer faces a diffi-cult task in identifying and acquiringthese often rare woods and specialist as-sistance is required The next question isto determine how the piece of furniturehas been surface-treated This entails theuse of analytical methods such as infra-red spectrometry gas chromatographyand X-ray fluorescence spectrometry toidentify the coatings and stains that havebeen applied In the present case (Fig 1)it was a matter of identifying the varnishon the wooden secretary shown in the fig-ure and determining the materials to beblended in order to replicate the varnishas accurately as possible The test resultsrevealed that the varnish was a complexmixture of natural raw materials specifi-cally a resin from an unidentified speciesof tree which had been boiled and dis-solved in linseed oilSelecting the correct analytical strate-

gy and evaluating the results demandsconsiderable experience The analysesrarely reveal complete formulations butthey do provide valuable partial resultswhich make it possible for the experi-enced restorer using his or her craft

932CHIMIA 2001 55 No 11

Fig 1 Wooden intarsia from a secretary

Fig 2 Chancelof the monasterychurch at MOstairwith Romanesquefrescoes over Ca-rolingian wall paint-ings

ART AND CHEMICAL SCIENCES 933CHIMIA 200155 No 11

Fig 3 Sword from Singen Germany 8th century Be with marks of areas for metallographicsections Length 53 em

skills to test replicated formulations un-der practical conditions in the workshopThe Miistair monastery complex

classified as a World Heritage Site is un-der the protection of UNESCO Wallpaintings have been uncovered in thechurch of St Johann which go back toCarolingian times (9th century AD)when the monastery was founded Dur-ing the Romanesque period these werecovered with new paintings The originalCarolingian painting can be seen at thebottom right of the picture of the chancel(Fig 2) while the upper painting is Ro-manesque Methods of analytical chemis-try are being used in an attempt to identi-fy the materials used in creating thesefrescoes Materia] is being lost from thewall paintings due to flaking of the paintlayer and microbia] decay The presenceof protein residues on the surface was re-vea]ed by means of gas chromatographymass spectrometry (amino acids) andplasma emission spectrometry (phos-phates) They are attributable to the ca-sein frequently used in tempera In thisproject analytical chemistry assists themicrobiologist and acts as a decision-making too] for the restorer The investi-gations are still underway Knowledge ofthe paint formulations makes it possiblefor the restorer to replicate similar formu-lations in the workshop Laboratory andoutdoor weathering tests then revealwhether the replicated formulations arestable over the long term At presenttempera paints are being tested and artifi-cially aged on sample plates This ap-proach ensures that our descendants willbe able to enjoy the original Romanesqueand Carolingian paintings for as long aspossibleEMPA Diibendorfs CorrosionSur-

face Protection Section is currently in-vestigating a product which should beuseful for art conservation Tests are be-ing carried out on a plant-derived conso]-idation agent named funori (po]ysaccha-ride) which is obtained from red seaweedof the genus Gloiopeltis and has beenused in Japan for centuries in paper resto-ration Preliminary tests in the conserva-tion and restoration workshop for paint-ings and sculptures of the Swiss Nationa]Museum have shown that chalky mattpaintings on various substrates can success-fully be consolidated with funori withoutthe optical surface changes such as un-wanted gloss fogging or darkening whichoccur with other consolidation agentsIn the project tests were conducted on

models to investigate ageing and the riskof possible salt efflorescence Testingwas performed using an accelerated

weathering device with exposure to UVradiation and a condensing atmospherewhich is normally used to test industrialcoatings such as automotive paints butwhich was modified and adapted to therequirements of these much more sensi-tive specimens The Biology Section atEMPA St Gallen has tested funoris sus-ceptibility to attack by microorganismsand established that it bears comparisonwith other consolidation agents In sum-mer 1999 a collaborative field test withrestorers working on the decorativepainting of the St Andreas charnel housechapel at Kerns in the canton of Obwa]-den confirmed the positive laboratoryand workshop findings [1] In order to geta clearer picture of the various productsthat are available under the name funorimaterials from various suppliers were in-cluded in the investigation The varia-tions in quality revealed by this investi-gation make it difficult to introduce thisconsolidation agent in its current form inconservation work despite its very goodperformance This variability encouragedus to pursue the production of a standard-ised seaweed-based product A highquality seaweed-based product would bea valuable addition to the conservatorre-storers toolbox for consolidating mattpaintings

3 Inorganic materials

Since metals are the principal inor-ganic materials investigated in an archaeo-metric context at EMPA the followingdiscussions focus on them Other materi-als such as slags and pigments are inves-tigated only occasionally The InorganicAnalytical ChemistryCharacterization ofSolids Section has a long tradition of re-search in metals Apart from the detec-tion of forgeries most analytical work onmetals relates to elucidating manufactur-ing processes determining provenanceand to restoring and conserving meta] ar-tefacts

31 IronVarious individual studies address all

the above issues in relation to iron

EMPA has long been helping to deter-mine the shape of iron finds which itsX-ray experts have systematically radio-graphed on behalf of the Swiss Nationa]Museum prior to restoration and conser-vationCorrosion experts have contributed to

conservation matters eg with an inves-tigation into the passivation of chloridesin the corrosion layer of iron in the 1980s[2] They discovered that the most impor-tant component in rusting is the iron hy-droxide akaganeite (~-FeO(OH)) whichis only formed in the presence of ch]o-rine It has a catalytic effect on the rate ofcOlTosion of iron even in the presence oflow levels of humidity and cannot becompletely removed from the corrosionlayer It was concluded that no restonl-tion or conservation method is capable oftotally reducing the chloride content overthe long term and that only storage at lowatmospheric humidity after conservationcan to a certain extent guarantee long-term preservation In the 1990s metallur-gists investigated the behaviour of certainsteel microstructures during plasma con-servation The investigation revealed thatmicrostructure whether obtained byhardening or by cold working is not de-stroyed by plasma conservation as ap-plied today because it proceeds at a tem-perature below the microstructure trans-fornlation temperatureThe history of iron goes far back into

antiquity the oldest finds dating back tothe 4th millennium BC in Asia Minorwhere the production of iron became es-tablished in the 2nd millennium BC as inAfrica In the I st millennium BC ironproduction spread to Europe and ChinaIn the 1980s metallurgists at EMPA

investigated one of central Europes old-est swords (Fig 3) dating from the 8thcentury BC [3] The metallographic in-vestigation revealed that the sword bladewas produced by piling (Fig 4) a methodthat is a precursor of pattern-welding atechnique in which the layers are addition-ally folded or twisted Carbon dispersionis ilTegular showing that the technique ofcarburisation had not yet been masteredIn the 1990s further iron objects were in-


Fig 4 Optical micrograph of the cross sectionetched by Nital of the mark B on the sword fromSingen At the top the partially opened princi-ple welding The sword is constructed by edge-to-edge banding The carbon content variesbetween 00 and 08 Darker parties arecarbon richer

vestigated in a collaborative project withthe Department of Prehistory at the Uni-versity of Ziirich and the Swiss NationalMuseum one of which was a spear fromthe Iron Age hoard from Wartau Ochsen-berg in the canton of St Gallen [4] Themetallographic investigation revealedthat this likewise piled object had beenexposed to thermal change after its pro-duction a finding which confirmed thearchaeologists suspicion that this hoardwas a burnt offeringAt around the same time archaeo-

metallurgists began to seek out methods ofchemically characterising historic ironwith its high content of inclusions so asto be able to determine its provenanceLaser ablation inductively coupled plas-ma mass spectrometry (LA-ICP-MS)proved to be an ideal method as it can beused for selectively measuring small por-tions of a surface (in this case 80-100 -Ill

across 35-45 -Ill deep ablated mass es-timated around 05-1 )lg) Craters of asmaller size could be obtained but small-er craters would decrease the relativesensitivity and are considered to be lessrepresentative of the iron composition[5][6] EMPAs development of the ca-pabilities of its instrumentation openedup a new application in the form ofarchaeometallurgy providing archaeolo-gists with the answer to a burning ques-tion Although it has not yet been possi-ble to use this method to determineelements such as nitrogen and sulfurwhich are important to the material char-acteristics of iron it has proved possiblein the case of the early medieval nowabandoned hamlet of Develier-Courte-telle in the canton of Jura to determinewhich iron objects were produced locally(an example is shown in Fig 5 and 6)Develier-Courtetelle was a settlementwhich specialised for a time in smithingExcavations have uncovered one ofEuropes largest quantities of smithingslags EMPA has been investigatingwaste and products from this smithy forfour years in ajoint research project withthe canton of Jura A thesis relating to thematerial characteristics and the mannerof fabrication of iron objects from theIron Age to the early medieval periodwill shortly conclude this research [7]

934CHIMIA 2001 55 No 11

Fig 5 Early medieval locally produced chiselfrom Develier-Courtetelle canton of JuraLength 93 cm (Photo Office du patrimoinehistorique jurassienne Section darcheologie)

Fig 6 The optical micrograph of the cross section etched by Nital shows the welded-on tip ofhypoeutectoid steel from the chisel The tip is constructed by surface-to-surface banding Thecircles mark the areas to be analysed by LA-ICP-MS


32 Copper and BronzeSince the mid 1980s EMPA has been

actively involved in a first major projectusing plasma emission spectrometry(ICP-OES) to characterise chemically athousand archaeological bronze objectsfrom Switzerland Analysis of the majorand minor elements revealed the devel-opment of copper alloys over an entiremillennium from 1800-800 BC [8] 1993saw a collaborative investigation with theSwiss National Museum and the archae-ology department of the canton of Zurichinto the composition of Roman and medi-eval bronze taps Analysis by ICP-OESand metallography revealed that the ma-terials were of moderate quality corre-sponding to an everyday mass-producedarticle No criteria for distinguishing be-tween Roman and medieval nonferrousmetals could be identified EMPAs firstforay into the experimental archaeologyof nonferrous metals involved X-rayfluorescence (XRF) and metallographicanalyses of an experimentally recastBronze Age sword to investigate possiblegravity segregation

1997 saw the beginning of intensivecollaboration with archaeological institu-tions researching copper smelting in an-tiquity The first step involved analysis ofancient copper smelting slags from Cy-prus Variations in the composition of themajor elements of individual slag flowswithin the same furnace batch were iden-tified [9] As a follow-up ores slags andmetals from prehistoric copper smeltingat Oberhalbstein in the canton of Grisonswere investigated in collaboration withthe archaeology department of the SwissNational Museum for their trace elementcomposition by XRF As a result of this

investigation it was possible to rule outthe hypothesis that fahlores (compoundsof copper with arsenic antimony andsulfur (Cu Ag)lo(Fe Znh(Sb AS)4S13)were smelted at Oberhalbstein and toconclude firmly that the prehistoric cop-per was produced by smelting chalcopy-rite (copper iron and sulfur CuFeS2)[10] The same year saw the beginning ofinvestigations into metallic materials andwaste products from the archaeologicalexcavations at the monastery complex ofSt Johann at Mtistair canton of GrisonsThe aim was to provide a comprehensivechemical and metallographic characteri-zation of these materials Only once theinvestigations were under way did thefocus move to the bronze wastes with ahigh tin content which indicate syste-matic recycling and reuse of broken bellsA year ago a project was started as

part of a thesis in archaeometallurgy toevaluate the excavations of the only com-pletely recorded site of ancient copperproduction on the copper island ofCyprus [II] Analyses of ores slags fur-nace residues and metals are currentlyunderway at EMP AOne example which may be men-

tioned is the ICP-OES analysis of rawcopper finds from two sites on CyprusThe significant difference in the concen-trations of minor elements (Fig 7) provesthat two different ore bodies were beingexploited the purer metal was obtainedfrom unaltered chalcopyrite in a stock-werk mineralisation deposit The lesspure metal with a higher content of silverarsenic lead antimony tin and zinc indi-cates the exploitation of zones of secon-dary enrichment in a massive sulfide orebody Investigations into possible frac-

935CHIMIA 200155 No 11

tionation of the lead isotopes in all thematerials of the production chain are tobe carried out in cooperation with variouslaboratories Experimental reconstruc-tion of the smelting furnaces is intendedto elucidate the production process [12]By using the most authentic raw materi-als and tools possible for the experimentand then subjecting the products of theexperiment to the same series of analysesas the archaeological finds the intentionis to test the archaeological hypothesesagainst the results of the experiment

33 Silver and GoldThe question of authenticity frequent-

ly arises with noble metals Art expertshave various criteria at hand to assess theauthenticity of silver or gold antiquitiesForgeries or stylistic copies may often beidentified as such solely by a thoroughvisual inspection of the method of pro-duction on the basis of stylistic featuresby hallmarks or traces of wear Faithfulcopies or forgeries of high quality mayhowever appear deceptively authenticeven to a practised eye It is on the otherhand very difficult to reproduce thecharacteristic composition of the traceelement contaminants present in old sil-ver or gold The contents of these traceelements are in fact mainly dependentupon the metallurgical refinement pro-cess used for the noble metalIn the early 1990s EMPA was com-

missioned to examine four gold dishesprior to an auction of pre-Columbianworks of art A trace analysis by plasmamass spectrometry of tiny chips of goldtaken from these objects revealed elevat-ed mercury contents indicating that thegold was obtained using the amalgama-

10000Almyras Sia-Anogia

1000~~c 1002eE~ 010c00

0Q1

000 Ag As Ni Pb Sb Sn Zn Fe S

Fig 7 Distribution of minor elements in cop-per determined by ICP-OES (plasma emissionspectrometry) from the two Cypriot coppersmelting sites Almyras and Sia-Anogia


tion process which was unknown to thepre-Columbian Indians As a result thefour objects were withdrawn from theauctionIn recent years an antiques dealer

has commissioned tests of the authenticityof various silver statuettes and drinkingvessels mainly dating from the 16th and17th centuries The 19th century saw theintroduction of new metallurgical pro-cesses which substantially altered thetrace element composition of silver alloysThanks to the LA-ICP-MS method men-tioned above in relation to iron it is pos-sible to carry out virtually non-destruc-tive tests to verify whether the trace ele-ment contents of a silver alloy corre-spond to the period before or after the19th century [13] (Fig 8) To this endthe trace sample is compared with a con-stantly growing in-house database ofEuropean silver artefacts from the 16th to20th centuries This method has made itpossible to detect various forgerieswhich could have damaged the dealersgood reputation had they been sold onThe same analytical method was also

used to investigate fragments of a spiralring from a grave in Sion canton of Val-ais which dates back to 2400 BC [14]To date this is Switzerlands most an-cient noble metal find In this case thepurpose of the analysis was not to deter-mine the authenticity of the object as thiswas not in question but instead to deter-mine whether it was made from naturalnative silver or from smelted cupelledsilver The metals relatively high con-tent of the companion element lead

(02) in comparison to native silver(0001-001 Pb) would tend to indicateproduction by a cupellation process froma lead ore During cuppellation the lead-silver mixture smelted from ore is heatedin a flat hearth (cupella) into an oxidisingatmosphere Lead changes in lead oxide(litharge) and silver remains as unalteredfluid metal

34 Determining the Provenance ofLead PigmentsNatural lead consists of the four stable

(non-radioactive) isotopes 204Pb 206Pb207Pb and 208Pb In terrestrial lead thelatter three isotopes are partly the endproduct of the radioactive decay series ofthorium and uranium whereas 204Pb isnot radiogenic in origin The relativeabundances of the lead isotopes in a lead-bearing ore deposit and in the productsderived from that ore depend on the ini-tial U and Th concentrations in the parentore and on the age of the ore bodyHence the lead isotope composition ofnatural ore deposits shows regional varia-tions which can be used to determine thegeographical provenance of artefactscontaining leadIt is possible for instance to trace the

geographical origin of historical leadpaints on works of art by lead isotopeanalysis In combination with the deter-mination of naturally occurring trace im-purities eg silver manganese and anti-mony the origin of the lead in white leadpaint can be pinpointed almost exactlyUsing EMPA St Gallens multicol-

lector inductively coupled plasma mass

936CHIMIA 2001 55 No 11

spectrometer (MC-ICP-MS) isotope ra-tios can be determined with great accura-cy and precision (Srel(1 )= 0002 - 001 )and trace impurities can be measureddown to a concentration of about onelgg of material This method has beenused to analyse J1g amounts of lead whiteon renaissance and baroque paintings Inthis way it has been possible to distin-guish historical white lead paint fromFlanders from Italian white lead andmodern white lead from historical whitelead Fig 9 shows a scatter plot of leadisotope ratios in four white lead samplesfrom renaissance paintings and threemodern white lead samples The lead iso-tope pattern in white lead from the sam-pled renaissance paintings differs signifi-cantly from the pattern in modern whitelead because modern white lead comesfrom other ore sources than historicallead a fact which can be used to detectmodern additions and forgeries

4 Conclusions

The various investigations clearlydemonstrate that archaeology and theconservation and restoration of culturalheritage derive great benefit from the sci-ences with close collaboration being es-sential to mutual understanding Thiswork is of course not the daily bread andbutter of a materials testing and researchlaboratory This is an example of howdisciplines such as analytical chemistryand the characterization of solids must al-ways be ready to tackle new areas by

Fig 8 The alternative laser ablation cell used inthis work placed upon a silver statuette 1laser ablation cell 2 focussing lens 3 auto-focus 4 supporting platform


218

216 ~ 81-3

~ 0 214a(00C

0 212altXl bull0C

210A1middot4

208

206

11 111 112 113 114 115 116 117 118 119

206Pb207Pb

Fig 9 Scatter plot of the ratios 208Pbj206Pb versus 206Pbj207Pb A1-4 = historical white leadpigment 81-3 = modern white lead pigment

937CHIMIA 200155 No 11

seeking dialogue with other scientificdisciplines helping to find commonterms of referenceIn a extended understanding of the

science of materials it is thus desirable toknow about the history of materials pro-duction and that this knowledge will takeits place in researching modern materialswith regard to sustainability

Received September 19 2001

[1] F Michel Interdisziplinare Grundlagen-forschung zur Konsolidierung von matterMalerei EMPA Bericht Projekte 199949

[2] EMP A Bericht I 12271988[3] PO Boll TH Erismann WJ Muster

Metallkundliche Untersuchung einesfriihen mitteleuropaischen Eisenschwer-tes in Friihes Eisen in Europa Ed HHaefner Schaffhausen 198145-51

[4] PO Boll A Flisch M Senn-LuderArchliometallurgische Untersuchungenan keltischen Eisenwaffen von WartauOchsenberg (SG) in Prehistoric alpineenvironment society and economy Uni-versitatsforschungen zur prahistorischenArchaologie 55 Bonn 1999 283-288

[5] B Wanner Entwicklung von Probenein-fiihrungssystemen fUr die induktiv gekop-pelte Plasma-Massenspektroskopie zurSpurenelementanalytik mit kleinen Pro-benmengen EMPA report no 236Diibendorf 1996

[6] W Devos M Senn-Luder C Moor CSalter Laser ablation inductively cou-pled mass spectrometry (LA-ICP-MS) forspatially resolved trace analysis of early

medieval archaeological iron finds Fre-sen ius J Anal Chem 2000 366 873-880

[7] M Senn Bischofberger Das Schmiede-handwerk n6rdlich der Schweizer Alpenvon keltischer Zeit bis ins Friihmittelal-ter Dissertation University Zurich 2002(in progress)

[8] V Rychner N Klantschi Arsenic Ni-ckel et Antimoine Cahiers d archeologieromande No 63 Lausanne 1995

[9] W Fasnacht S Schwarzlander P BollThe Sia-Mathiatis-Agia Varvara surveyproject (SMASP) second preliminary re-port in Report of the Departement ofAntiquities Cyprus Nicosia 1997 219-224 Table 2

[10] W Fasnacht Prahistorischer Kupfer-bergbau im Oberhalbstein und dessenSpuren in der bronzezeitlichen SiedlungSavognin-Padnal (GR) in Prehistoric al-pine environment society and economyUniversitiitsforschungen zur prahistori-schen Archaologie 55 Bonn 1999 267-276

[11] The internationally coordinated project isentitled Archaeometallurgical investiga-tions of ancient copper smelting evidencein Cyprus The Site of Agia Varvara-Almyras (Swiss National Science Founda-tion project H Vonmont EMPA Section131 and W Fasnacht project leaderAlmyras Excavation 1999-2001)W Fas-nacht Excavations at Agia Varvara-Almyras A Review of Twelve Years ofResearch in Report of the Departmentof Antiquities Cyprus Nicosia 1999179-184

[12] W Fasnacht Zehn Jahre Kupfer- undBronzeguss im Experiment - oder diewiederholte Erfindung des RadesZeitschrift fur Schweizerische Archiiolo-

gie und Kunstgeschichte 2001 58( J) 67-70 Abb 1

[13] W Devos C Moor P Lienemann De-temlination of impurities in antique silverobjects for authentication by laser ablationinductively coupled plasma mass spec-trometry J Anal At SpectlOm 1999 14621-626

[14] P Boll Ein Spiralring aus Sion in Veli-ka Gruda I Universitlitsforschungen zurprahistorischen Archaologie Band 32Bonn 1996 ] I I-I 12


Two examples from the ChemistrySection of EMPA St Gallen illustratethis point When restoring furniture thequestion always arises of the identity ofthe materials that the craftsman used toproduce the piece The first question is toidentify the species of wood which de-fines the strength structure and colour ofthe furniture The restorer faces a diffi-cult task in identifying and acquiringthese often rare woods and specialist as-sistance is required The next question isto determine how the piece of furniturehas been surface-treated This entails theuse of analytical methods such as infra-red spectrometry gas chromatographyand X-ray fluorescence spectrometry toidentify the coatings and stains that havebeen applied In the present case (Fig 1)it was a matter of identifying the varnishon the wooden secretary shown in the fig-ure and determining the materials to beblended in order to replicate the varnishas accurately as possible The test resultsrevealed that the varnish was a complexmixture of natural raw materials specifi-cally a resin from an unidentified speciesof tree which had been boiled and dis-solved in linseed oilSelecting the correct analytical strate-

gy and evaluating the results demandsconsiderable experience The analysesrarely reveal complete formulations butthey do provide valuable partial resultswhich make it possible for the experi-enced restorer using his or her craft

932CHIMIA 2001 55 No 11

Fig 1 Wooden intarsia from a secretary

Fig 2 Chancelof the monasterychurch at MOstairwith Romanesquefrescoes over Ca-rolingian wall paint-ings





















934CHIMIA 2001 55 No 11










935CHIMIA 200155 No 11






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936CHIMIA 2001 55 No 11


4 Conclusions




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216 ~ 81-3

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208

206

11 111 112 113 114 115 116 117 118 119

206Pb207Pb


937CHIMIA 200155 No 11








































934CHIMIA 2001 55 No 11










935CHIMIA 200155 No 11






1000~~c 1002eE~ 010c00

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936CHIMIA 2001 55 No 11


4 Conclusions




218

216 ~ 81-3

~ 0 214a(00C

0 212altXl bull0C

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208

206

11 111 112 113 114 115 116 117 118 119

206Pb207Pb


937CHIMIA 200155 No 11



























935CHIMIA 200155 No 11






1000~~c 1002eE~ 010c00

0Q1












936CHIMIA 2001 55 No 11


4 Conclusions




218

216 ~ 81-3

~ 0 214a(00C

0 212altXl bull0C

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208

206

11 111 112 113 114 115 116 117 118 119

206Pb207Pb


937CHIMIA 200155 No 11





























936CHIMIA 2001 55 No 11


4 Conclusions




218

216 ~ 81-3

~ 0 214a(00C

0 212altXl bull0C

210A1middot4

208

206

11 111 112 113 114 115 116 117 118 119

206Pb207Pb


937CHIMIA 200155 No 11





















218

216 ~ 81-3

~ 0 214a(00C

0 212altXl bull0C

210A1middot4

208

206

11 111 112 113 114 115 116 117 118 119

206Pb207Pb


937CHIMIA 200155 No 11




















An Odyssey Through Time at EMPA

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