Pigment traces on medieval stonework in Gotland’s churches – examination of seven 12th century baptismal fonts and a limestone pew Anders G. Nord et al. http://kulturarvsdata.se/raa/fornvannen/html/2016_017 Fornvännen 2016(111):1 s. 17-26 Ingår i samla.raa.se Art. Nord et al 17-26_Layout 1 2016-02-15 16:52 Sida 17

Pigment traces on medieval stonework in Gotland’s churches –examination of seven 12th century baptismal fonts and a limestone pew

By Anders G. Nord, Kate Tronner, Kjell Billström and Marianne Gustafsson Belzacq

Nord, A.G., Tronner, K., Billström, K. & Gustafsson Belzacq, M., 2016. Pigment traces on medieval stonework in Gotland's churches – examination of seven 12th century baptismal fonts and a limestone pew. Fornvännen 111. Stockholm.

The authors have analysed pigments on eight medieval stone objects in Gotland’s churches. They are seven 12th century baptismal fonts made of sandstone and a ce­ remonial limestone pew in Burs church from about 1350. Fragments of medieval paint were sampled and analysed by SEM/EDX, FTIR, GC­MS and MC­ICP­MS. 57 samples were collected. Infinitesimal traces of cinnabar, ultramarine and gold foil were sparsely found. Iron oxide (Fe2O3) and lead pigments occur commonly, while green and blue pigments seem less frequent. Later “improvements” of green copper arsenites were found on the limestone pew in Burs church. Lime has prima­ rily been used as a binding medium, possibly in combination with now complete­ ly degraded organic substances. Isotope analyses indicate that the lead pigments most likely have a provenance in the Harz and Erzgebirge mountains in Germany, possibly also in Eisleben. Other pigments have more remote origins, which reflects Visby’s significance as a trade center.

Anders G. Nord, Kevingeringen 10, SE–182 50 Danderyd [email protected] Kate Tronner, Flädergränd 2, SE–187 73 Täby [email protected] Kjell Billström, Department of Geosciences, Swedish Museum of Natural History, Box 50007, SE–104 05 Stockholm [email protected] Marianne Gustafsson Belzacq, Gurpe 117 Kräklingbo, SE–623 70 Katthammarsvik [email protected]

Hundreds of medieval churches in Sweden have present study, we analysed original paint traces more or less well­preserved murals painted al secco from seven 12th century baptismal fonts made on lime ground. We have earlier documented and from sandstone and a ceremonial limestone pew analysed many of their pigments (Nord et al. 1996; from around 1350, all in Gotland’s churches, by 2000; 2011; 2015), and have so far identified 23 means of SEM/EDX and other techniques. The pigments (disregarding modern ones used for later aim of the study has been to identify pigments of “improvements”). Recently, we have extended our variousshadesandsearch forbindingmedia. While studies to include medieval stonework such as the stone itself is obviously of local origin, we have outdoor portals (Nord & Tronner 2014). For the tried to identify the origin of the pigments.

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18 Anders G. Nord et al. Fig. 1. The sandstone font in Barlingbo church, Got­ land, with a sculpture of the archangel Gabriel. Pho­ to: Bengt A. Lundberg, National Heritage Board of Sweden.

seems to have been the most productive. Roos­ val’s invented name Byzantios suggests a Russian­ Byzantine origin, but this has so far not been generally accepted by art historians. Presumably the name was suggested (Roosval 1918) by a cer­ tain stylistic elegance influenced by Byzantine murals. Sixteen fonts on Gotland, some of them in poor condition, have been attributed to Byzan­ tios. For the present study, the Hejde and Hogrän fonts were selected, rather from the presence of usable original paint than as typical representa­ tives of the Byzantios group. Another sculptor named Hegvald or Hegwaldr was in all likeli­ hood a local man from Gotland. His workshop has a more popular and provincial style, and Gotland has 92 well­preserved medieval stone three fonts were selected for this study, namely churches, in addition to ruined ones. Most of these those of Endre, Etelhem and Stånga. The Etel­ churches have a medieval baptis­mal font, made hem font is actually signed “Hegwaldr” in runes. from sandstone or limestone from local quarries. The Majestatis group, famous for their extreme Most fonts have been painted, and original paint skill in reliefs, is represented here by the font of can still be observed as infinitesimal traces. How­ Gerum. Roosval assigned this name because of ever, many fonts were re­decorated 300–400 years the group's habit of representing Christ as sover­ ago, which strongly reduced the number of eign ruler of the world (Majestatis domini). Final­ usable objects for the present study. ly, the Master of Barlingbo is only known to have Nearly a century ago, art historian Johnny made the font in Barlingbo church (fig. 1). This Roosval (1918; 1925) identified a number of sculp­ beautiful and imposing font is the largest one on tors or workshops, and named them Byzantios, the island. Majestatis, Hegvald, Calcarius, Sigraf, Egypticus All seven selected fonts have beautiful sculp­ etc. Many of these artisans seem to have worked tural decoration. The local sandstone they are made on Lund Cathedral before moving to the pros­ of consists mainly of quartz grains cemented to­ perous island of Gotland to work there. In his gether by calcium carbonate. The ceremonial pew 2012 survey of Gotland fonts, Svenrobert Lund ­ in Burs church however is made of local fine­ quist attributes each of 45 baptismal fonts to a grained limestone. It is probably a product of the specific group based on type, motif, decorations, Egypticus workshop. All paint traces for the study reliefs, chisels used, etc. These fonts include the were carefully sampled and documented. Many ones selected for the present study, and we use pigments could not be observed with the naked the attributions suggested by Roosval and Lund­ eye, but demanded a magnifying glass. When­ quist. It should also be added that the influential ever possible, we took somewhat larger samples Byzantine art of the same era in Sweden has been with the aim to search for binding media. In total discussed by for instance Andreas Lindblom & we collected 57 samples. Gunnar Svahnström (1959), Erland Lagerlöf (1999) and Svetlana Vasilyeva (2009). Among the sculptors, the Byzantios group

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Pigment traces on medieval stonework in Gotland’s churches 19 SEM/EDX analyses of the pigments and minium transforms to (usually) black platt­ Work began some years earlier with Kate Tron­ nerite (e.g. Giovannoni et al. 1990; Nord et al. ner identifying the pigments on the Barlingbo 1996). This transformation may be partial or font by means of wet chemistry and X­ray pow­ complete. In the former case the colour may der diffraction (XRD). All other pigment sam­ become dark brown or a mixture of dark shades. ples were analysed by SEM/EDX, i.e. with a scan­ This process seems to be slow as any rapid change ning electron microscope (Hitachi S­4300) equip­ to black candle flames and haloes on the murals ped with a LINK/Oxford unit for X­ray micro­ would have evoked a congregation’s righteous analysis, at the Swedish Museum of Natural His­ anger. The transformation process requires O2(g) tory. from the air as oxidizing agent. Co­author M.G.B., Tab. 1 lists the results of the pigment analy­ with a life­long experience of medieval murals, ses. The pigments identified accord well with has noted that minium can retain its red colour in those found on medieval stone portals (Nord & cavities covered and protected by plaster. Tronner 2014), although gold and ultramarine We have also found that sometimes the oxi­ were never found there. Tab. 2 offers further che­ dation does not take place in paintings on other mical and mineralogical data. The pigment PbO substrates. A striking example is found in the is denoted as massicot, whether from the natural church of Härkeberga in Uppland. In the narrow mineral or a synthetic product with that compo­ staircase leading to the organ loft, there is an sition. Furthermore, plattnerite (β­PbO2) is not image from around 1490 of a man, originally paint­ an original pigment but a product of the oxidation ed with minium to wear orange clothes. Part of of a lead pigment. Chlorine was detected in many the painting is on lime ground where plattnerite samples, probably representing remains of mod­ has formed, another part on oak timber where ern cleaning agents. On the Burs pew, “improve­ the minium is preserved (Nord & Tronner 2000). ments” of copper arsenites were found. These are Moreover, lead pigments on wood from the likelytorepresentSchweinfurtergreenandScheele’s (long­since demolished) medieval stave church of green, as judged from the Cu:As atomic ratios. Dalhem on Gotland still preserve their original Tab. 3 lists the pigments we found on the colour (Nord & Tronner 2011). fonts and the pew. Note that pigments that are Our study of the baptismal fonts yielded a now missing from an individual object may orig­ similar result. Plattnerite has almost always form­ inally have been there. Iron oxide was found on ed when lime is present (tab. 1). Thus it seems that most of the fonts, and so was minium and lead lime, or some substance(s) therein, acts as a kind white. The coeval workshops Byzantios, Hegvald of catalyst for the oxidation process. The “platt­ and Majestatis, to which the examined fonts have nerite problem” has been discussed by other been attributed, seem to have used similar pa­ authors. Petushkova & Lyalikova (1986) empha­ lettes. Fragments of gold, cinnabar and ultrama­ sized the influence of microorganisms for the oxi­ rine on some objects is consistent with the fact dation of lead pigments. Giovannoni et al. (1990) that Gotland was a prosperous island from the studied the oxidation process of lead white. They Iron Age through the Middle Ages. Note that concluded that an alkaline environment, mois­ generally green and blue pigments occur sparsely ture and microorganisms all seem to accelerate here compared to results obtained for medieval the oxidation process. Aze et al. (2007; 2008) in ­ ecclesiastical stone objects on the Continent (e.g. dicate light, humidity, microorganisms and sul­ Rossi­Manaresi 1981; 1984; Hauff 1988). On phurous air pollutants as important factors for these stone objects, malachite, azurite, ultrama­ the formation of plattnerite. Kotunalová et al. rine and cobalt glass (smalt) are common. (2009) stress inorganic salt as one of the most active agents. To sum up, lead pigments on a lime The plattnerite problem ground exposed to air, in combination with oth­ Let us look closer at plattnerite. Lead pigments er damaging factors, seem to be susceptible to painted on a ground of plaster (lime) often dark­ plattnerite formation. en over time. Accordingly, lead white, massicot

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20 Anders G. Nord et al.

Church Workshop Sample Colour Pigments identified

Hejde B 10A Red Iron oxide, lead white 10B Dark grey Plattnerite, lime 11 Reddish brown Iron oxide, minium, plattnerite 12 Orange Iron oxide, massicot, lead white 13* Black Plattnerite, lime 14* Black Plattnerite, lime

Hogrän B 5 Yellow Massicot, ochre, minium, lead white 6* Dark grey Plattnerite, lime 7* Orange Minium 8 Violet Caput mortuum 9 Yellow Massicot

Endre H 1A Black Plattnerite, lime 1B Red Iron oxide, lime 2 Yellow Orpigment 3 Dark grey Plattnerite 4A Red Cinnabar 4B Black Plattnerite, lime

Etelhem H 15 Reddish brown Iron oxide 16* Red Minium 17 Beige Orpigment, lead white 18 Yellow Orpigment 19 Blue Azurite, lead white 20 Pink Minium with some lime

Stånga H 35* Red Iron oxide, minium 36 Golden Gold 37 Blue­grey Ultramarine, lead white, lime 38 Reddish brown Iron oxide

Gerum M 28 Golden Gold 29 Pink Minium, lead white 30 Green Malachite, lead white 31 Red Cinnabar, minium 32 Grey Minium, plattnerite, lime 33 Grey to black Plattnerite, lime 34 Reddish brown Iron oxide

Barlingbo MB MB­1 Red Iron oxide, minium, gold MB­3 Blue Azurite MB­4 Blue Azurite, lead white, carbon black MB­6 Red Minium, lead white MB­8 White Lime MB­9 Red Minium, lime, gold MB­10 Blue Azurite, lead white MB­11 Red Minium, lead white MB­12 Pale green Green earth

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Pigment traces on medieval stonework in Gotland’s churches 21

Church Workshop Sample Colour Pigments identified

Burs (pew) E 21 Blue­green Atacamite, malachite, azurite, copper arsenite (cf. tab. 2) 22 Black Plattnerite, lime 23 Brownish black Plattnerite, minium, lime 24 Grey­black Plattnerite, lime 25* Black Plattnerite, lime 26 Blue­green Malachite, azurite 27 Green Atacamite

Table 1. Pigments (including oxidized plattnerite, β­PbO2) identified on seven baptismal fonts and a limestone pew. Abbreviations for the sculptors and the workshops (Workshop): B=Byzantios, H=Hegvald, M=Majestatis, MB=The Master of Barlingbo, E=Egypticus. The seven samples used for lead isotope analysis are marked with an asterisk (*).

Colour Name Chemical composition; mineralogical information

White Lime Calcium carbonate, CaCO3 Lead white Synthetic product 2PbCO3.Pb(OH)2. Also exists as the mineral hydrocerussite Black Carbon black C Plattnerite Lead dioxide, β­PbO2 (oxidized form of a lead pigment, i.e. not a natural pigment) Yellow Ochre Earth colour containing iron oxide(s) Massicot The mineral PbO (also exists as a synthetic product) Orpigment Mineral As2S3 Gold Au (natural product) Red Iron oxide Fe2O3 (natural or synthesized) Minium Synthetic product Pb3O4 Cinnabar Mineral HgS Violet Caput mortuum Violet modification of Fe2O3 Green Malachite Mineral CuCO3.Cu(OH)2 Atacamite Very rare mineral. Usually a synthetic form of Cu2Cl(OH)3 has been used Green earth Iron­rich pale green natural silicate Scheele’s green Synthetic product ~CuHAsO3 (18th century) Schweinfurter green Copperacetoarsenite, a pigment first produced around 1800 with (many synonyms exist) the formula Cu(CH3COO)23 Cu(AsO2)2. Later “improvements” Blue Azurite Mineral 2CuCO3.Cu(OH)2 Ultramarine Pigment from the mineral Lapis lazuli, with the approximate composition (Na,Ca)8(AlSiO4)6(S,SO4,Cl)

Table 2. Pigments found on the examined medieval objects, with some chemical and mineralogical data.

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22 Anders G. Nord et al.

Church Hejde Hogrän Endre Etelhem Stånga Gerum Barlingbo Burs

Workshop B B H H H M MB E Lead white X X X X X X Plattnerite X X X X X Massicot X X? Ochre X Orpigment X X Gold X X X Iron oxide X X X X X Minium X X X X X X Cinnabar X X Caput mortuum X Malachite X X Atacamite X Green earth X Azurite X X X Ultramarine X

Table 3. Summary of pigments detected on seven fonts and a limestone pew. Abbreviations for the workshops as in tab. 1. Lime is not included in the table. Nor are the copper arsenite “improvements” on the Burs pew.

Organic binding media Lead isotope data and possible origins We analysed six samples with a Perkin Elmer of the pigments Spectrum­100 FTIR spectrometer at the Royal We are interested in the origin of these medieval Institute of Technology in Stockholm, aiming to pigments. Common ones like green earth and search for organic binding media. Another larger iron oxides were most likely collected locally. All sample from the pew we sent to the Institut Roy­ other pigments listed in tab. 3, including gold, al du Patrimoine Artistique (IRPA) in Brussels must have been imported. Primarily this import for GC­MS analysis (PolarisQ and Tripel­TOF involved countries in central and south Europe. 5600 instruments). These attempts to trace Since Visby was an important commercial centre organic binding media, e.g. proteinous glue, lin­ during the Middle Ages, most pigments could seed oil or wax, all known to have been used on probably be bought from merchants there. Obvi­ medieval artefacts, were not fruitful. The FTIR ously even ultramarine (from the blue mineral analyses only indicated the presence of calcium lapis lazuli), which was notably only found in carbonate in addition to the pigments. The larg­ Afghanistan at that time, was available. er sample from the limestone pew, analyzed at As regards lead, its stable isotopes have long IRPA, contained low concentrations of stearic been used by archaeologists to reveal the origin and palmitic acid, as well as traces of the proteins of the metal. The stable isotopes 206Pb, 207Pb and keratin and trypsin. However, these organic sub­ 208Pb form by decay of uranium and thorium, stances may be contaminations from later activi­ whereas 204Pb is a stable, non­radiogenic isotope. ty. We conclude that lime was used as a binding (Their relative isotopic abundance is usually giv­ medium, and that any additional organic sub­ en by various ratios. For instance, 206Pb/204Pb, stances which may have been used have long­ 207Pb/204Pb and 208Pb/204Pb are used in geolo­ since deteriorated and are no longer possible to gical literature, while 207Pb/206Pb and 208Pb/ detect. 206Pb are more commonly seen in archeological applica­tions). The decay is extremely slow, and

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Pigment traces on medieval stonework in Gotland’s churches 23

Sample Worksh Pigment 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb 207Pb/206Pb 208Pb/206Pb

Hejde­13 B Plattnerite 18.458 15.617 38.375 0.8460 2.0794 Hejde­14 B Plattnerite 18.453 15.620 38.410 0.8464 2.0815 Hogrän­6 B Plattnerite 18.456 15.621 38.368 0.8464 2.0795 Hogrän­7 B Minium 18.407 15.612 38.329 0.8481 2.0828 Etelhem­16 H Minium 18.473 15.623 38.397 0.8456 2.0788 Stånga­35 H Minium 18.492 15.634 38.424 0.8453 2.0779 Burs­25 E Plattnerite 18.347 15.625 38.201 0.8559 2.0929

Table 4. Lead isotope data obtained for seven lead pigments. Abbreviations for the workshops as in tab. 1. Most samples were run in duplicate and analytical errors (2 σ of the mean) are ±0.10%, or better, for ratios involving 204Pb, and c. ±0.04% for the remaining ratios.

so the relative isotopic abundances depend on the isotope data indicate origins in much younger geological age of the ore and the conditions Palaeozoic to Mesozoic (545–65 Ma) deposits. under which it was mineralised. This forms the Using this information to determine the ori­ basis for using lead isotope data as a fingerprint gins of the lead is difficult. Lead isotope data have for the origin of lead. Many studies have been not been published for all possible ore districts. undertaken on archaeological metal artefacts Also the isotopic fingerprints of some ore dis­ with lead as an alloying element, such as bronze tricts overlap. The data are graphed in fig. 2. The objects and silver coins. A few studies of lead pig­ samples Hogrän­7 and, particularly, Burs­25 with ments have also been published (e.g. Brill et al. 206Pb/204Pb=18.347, are slight exceptions, whilst 1997; Fortunato et al. 2005; Nord et al. 2015). the other five samples have uniform composi­ In the present study, seven lead pigment sam­ tions with 206Pb/204Pb clustering around 18.46. ples large enough for an isotope study were ana­ The small deviations among the isotope ratios lysed at the Swedish Museum of Natural History indicate that all probably originate from a re­ with a MC­ICP­MS spectrometer (Microsoft Iso­ stricted area. This is consistent with the fact that probe). These samples contained minium (Pb3O4) all seven baptismal fonts were made during the and/or its oxidized transition form plattnerite. 12th century, involving contemporary sculptors, They were analysed following standard proce­ who bought pigments from merchants trading dures according to Ling et al. (2013). The results painting materials from only a few ore districts. are summarised in tab. 4. The values for the seven In a previous lead isotope study (Nord et al. samples are similar. 2015), 28 pigment samples from medieval murals The data show that none of these lead pigments (c. 1150–1500) in Swedish churches, seven of them originate from ore in the Bergslagen region of on Gotland, were analysed. The provenancing Sweden (the principal medieval mining district, indicated Germany as the most likely origin. This in the middle of Sweden). This ore district is geo­ tentative conclusion was based on the following logically very old, around 1900–1800 million years facts. 1) With few exceptions, the lead isotope (Ma), and its lead ores display a narrow range of data of the 28 samples matched well with data isotope ratios, with 206Pb/204Pb clustering around published for ore mined in the Harz and Erzge­ 15.70. This is quite different from the analysed birge regions (Niederschlag et al. 2003). 2) The samples with ratios in the range 18.34–18.49. Swe­ nearest large ore districts were in Germany. 3) dish lead was thus certainly not used for the pig­ Secondary minerals found in malachite inde­ ments identified in the present study. Instead the pendently indicated German ores (Nord et al.

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24 Anders G. Nord et al.

Fig. 2. Lead isotope data plotted as 208Pb/206Pb versus 207Pb/206Pb for lead pigments from the baptismal fonts (circles) and the limestone pew (bold circle). Reference data (Niederschlag et al. 2003) from various ore districts in Germany are included. (Eis=Eisleben, Erz=Erzgebirge).

2012). 4) Many medieval painters in Sweden in Germany at this time was restricted to only a were Germans or influenced by German art. few areas. Based on published mineralogical data Thus it seems that in 1150–1500 lead pigments (Wittern 2001) and lead isotope data (Lévêque used in Sweden most likely originated mainly & Haak 1993; Niederschlag et al. 2003; Monn et from Germany. al. 2008), we conclude that the Harz and Erzge­ The present study’s results also point towards birge are the most likely origins for the lead pig­ German ore districts. A number of criteria, such ments, but the nearby Eisleben district is also a as mining history, metal content and lead isotope likely candidate (cf. fig. 3). The isotope match data, are necessary to identify the most likely with these ores is good (cf. fig. 2). Note that the mining districts for the seven samples. A candi­ present isotope data for the Burs pew, made by date must of course have been mined during the Egypticus, are similar to two lead pigments from 12th century, and mined mainly for lead ore. murals in Lye Church, also painted by Egypticus According to Niederschlag et al. (2003), mining (Nord et al. 2015).

Fig. 3. Map of northern Europe indicating some possible sources of pigments. E=Eisleben, K=Kams­ dorf (a less likely source for the pigments). V=Visby, B=Berlin.

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Pigment traces on medieval stonework in Gotland’s churches 25 Conclusions Aze, S., Valler, J.M., Detalle, V., Grauby, O. & Baron­ None of our lead pigment samples originates from net, A., 2008. Chromatic alterations of red lead a Swedish mine. The lead mines of Bergslagen pigments in artwork: a review. Phase Transitions 81. Yverdon. were worked already from AD 900, but during Brill, R.H., Felker­Dennis, C.C., Shirahata, H. & Joel, the Middle Ages the miners probably did not E.C., 1997. Lead isotope analysis of some Chinese know how to prepare lead pigments, or did not and central Asian pigments. Agnew, N. (ed.). Con­ find it commercially profitable. With current servation of Ancient Sites on the Silk Road. Los Ange­ knowledge, the most likely conclusion seems to les. be that the lead originates from Germany, prob­ Fortunato, C., Ritter, A. & Fabian, B., 2005. Old mas­ ters’ lead white pigments: investigations of paint­ ably from the Harz and Erzgebirge but possibly ings from the 16th and 17th centuries using high also from Eisleben. This is also in agreement with precision lead isotope abundance ratios. Analyst earlier results (Nord et al. 2012; 2015) and the 130. London. fact that many Swedish churches were painted by Giovannoni, S., Matteini, M. & Moles, A., 1990. Stu­ Germans, or in a German style. dies and developments concerning the problem of altered lead pigments in wall paintings. Studies in As regards the other pigments identified on Conservation 35. London. the examined objects, common pigments were Hauff, G., 1988. Study and conservation of the poly­ probably obtained locally. Azurite and malachite chrome portal sculptures of the Holy Cross min­ are rare in Swedish bedrock and must have been ster in Schwäbisch Gmünd. Ciabach, J. (ed.). VIth imported. During the Middle Ages, cinnabar was International Congress on Deterioration and Conserva­ mainly mined in Spain and the western Balkans. tion of Stone. Torun. Kotulanová, E., Bezdička, P., Hradil, D., Hradilová, J., The merchants of Visby, an important member­ Svarcová, S. & Grygar, T., 2009. Degradation of town of the Hanseatic League, provided cinnabar, lead­based pigments by salt solutions. Journal of orpigment, ultramarine and gold from southern Cultural Heritage 10. Amesterdam. Europe or Asia. Or these materials were brought Lagerlöf, E., 1999. Gotland och Bysans. Bysantinskt infly­ to Gotland by foreign painters. Thus while the tande på den Gotländska kyrkokonsten under medelti­ sandstone for baptismal fonts was quarried locally, den. Visby. Lévêque, J. & Haak, U., 1993. Pb isotopes of hydro ­

the pigments for their decoration have quite a thermal ores in the Harz. Monograph series on Mine­ diversebackground.This showsthattradebetween ral Deposits 30. Berlin. Gotland and the European continent was well Lindblom, A. & Svahnström, G., 1959. Gotländska sten­ developed already around AD 1150. mästare. Malmö. Ling, J., Hjärtner­Holdar, E., Grandin, L., Billström, Acknowledgements K. & Persson, P.O., 2013. Moving metals or indige­ nous mining? Provenancing Scandinavian Bronze

Thanks to the Berit Wallenberg Foundation for a Age artefacts by lead isotopes and trace elements. generous research grant (BWS­2013.0010), to Journal of Archaeological Science 40. London. the staff of the Swedish Museum of Natural His­ Lundquist, S., 2012. Medeltida stenmästare och dopfuntar tory (Stockholm) for valuable help with the ana­ på Gotland. Romanska skedet, 1100–1200­talen. Burgsvik. lytical instruments and comments on our manu­ Monn, F., Hamer, K., Lévêque, J. & Sauer, M., 2008. script, and to Marina van Bos (IRPA, Brussels) Pb isotopes as a reliable marker of early mining and smelting in the Northern Harz province (Lower for her analytical contribution with the Burs Saxony, Germany). Journal of Geochemical Explo­ sample. Thanks finally to all the parishes involv­ ration 68. Amsterdam. ed for their kind help with sampling and docu­ Niederschlag, E., Pernicka, E., Seifert, Th. & Bartelheim, mentation. M., 2003. The determination of lead isotope ratios by multiple collector ICP­MS: a case study of Early Bronze Age artefacts and their possible relation References with ore deposits of Erzgebirge. Archaeometry 45. Aze, S., Valler, J.M., Pomey, M., Baronnet, A. & Grauby, Oxford. O., 2007. Red lead darkening in wall paintings: Nord, A.G. & Tronner, K., 2000. Chemical analysis of natural ageing of experimental wall paintings versus mediaeval mural paintings in Sweden. Goupy, J. & artificial ageing tests. European Journal of Mineralogy Mohen, J.P. (eds). Art et Chimie la Couleur, Actes du 19. Stuttgart. Congrès CNRS 1998. Paris.

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26 Anders G. Nord et al. – 2011. Kemisk analys av fjorton medeltidskyrkors logical degradation of lead­containing pigments. muralmålningar. Fornvännen 106. Studies in Conservation 31. London. – 2014. Färganalys av fem gotlandskyrkors portaler Roosval, J., 1918. Die Steinmeister Gottlands. Stockholm. och muralmålningar. Fornvännen 109. – 1925. Revision av gotländska dateringar. Fornvän­ Nord, A.G., Tronner, K. & Björling Olausson, K., nen 20. 2012. Copper vanadate minerals found in mediae­ Rossi­Manaresi, R., 1981. The polychromy of the 13th val mural paintings. Studies in Conservation 57. Lon­ century stone sculpture in the façade of the Ferrara don. Cathedral. ICOM Committee for Conservation, 6th Nord, A.G., Tronner, K., Nisbeth, Å. & Göthberg, L., triennial meeting, Ottawa, 21–25 September 1981: pre ­ 1996. Färgundersökningar av senmedeltida kalk­ prints. Paris. måleri – Härkeberga, Täby, Härnevi och Risinge – 1984. The polychromy of the portals of the Gothic kyrkor. Konserveringstekniska Studier 12. Stockholm. Cathedral of Bourges. ICOM 7th triennial meeting, Nord, A.G., Billström, K., Tronner, K. & Björling Copenhagen, 10­14 September 1984: preprints. Paris. Olausson, K., 2015. Lead isotope data for prove­ Vasilyeva, S., 2009. Bysantinska traditioner i Gotlands nancing mediaeval pigments in Swedish mural konst under 1100­talet. Fornvännen 104. paintings. Journal of Cultural Heritage 16. Amster­ Wittern, A., 2001. Mineralfundorte in Deutschland. Stutt ­ dam. gart. Petushkova, J.P. & Lyalikova, N.N., 1986. Microbio­

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