Križnar, Anabelle

Ruiz Conde, Antonio

Sánchez Soto, Pedro José

English

idUS. Depósito de Investigación Universidad de Sevilla

77macla. nº 18. enero´14workshop “Mineralogía Aplicada”Mineralogy of Supports andSelected Pigments inMediaeval Churches ofSlovenia/ ANABELLE KRIZNAR (1)* / ANTONIO RUÍZ-CONDE (2) / PEDRO J. SÁNCHEZ-SOTO (2)INTRODUCTIONMortar in ancient structures is a compo-site material which has exhibited exce-llent durability through time. It is consti-tuted of a binder, such as lime (CaO)and/or gypsum, and aggregates, suchas sand, grit, marble or lime-rock. Thecomposition of mortars varies greatlyand they are commonly divided intolime, gypsum and mixed ones, depen-ding on the binding material. The mostcommon one is lime mortar, in whichslaked lime is used as a binder. The cal-cination of calcite rock (calcium carbo-nate, CaCO3) at 800-900°C producesburnt lime (calcium oxide, CaO) and,after cooling, the hydration process oflime yields the hydroxide Ca(OH)2 alsoknown as slaked lime. After a carbona-tion process in air, the hydroxide in themortar yields calcium carbonate agan. Fresh mortar is the basic ground for afresco wall painting, a painting techni-que in which only natural inorganic pig-ments - earths and minerals, can beused. After drying, slaked lime evolvesthe pigment particles, converting alltogether in a hard and durable surface,which is one of the principle characteris-tics of mural painting. (Wehlte 1967,Knoepfli et al. 1990, Brachert 2001,Mora et al. 2001)OBJECTIVESThe present research was dedicated tothe analysis of selected murals from dif-ferent parts of Slovenia, covering theperiod from the 13th till the 15th centu-ries (Höfler 1996-2004). The principalobjective was to obtain information onthe composition of mortars and pig-ments applied. Among the pigments,only mineral ones were selected, asmalachite, azurite or cinnabar. Due totheir high cost, they can be rarely foundon Slovene murals.ANALYTICAL METHODSAll the paintings were first studied insitu, next, samples of mortars and pig-ments were carefully extracted. Theywere analysed by different analyticaltechniques (Matteini, Moles 1984,Kriznar 2006), prepared as finely groun-ded powder or as cross-sections. Theprincipal exam for the mortar composi-tion was carried out by X-ray Diffraction(XRD), a Siemens D-501 diffractometerwith CuK (α) Ni-filtered radiation. Theresults provided the information aboutcrystalline phases of mortars as well asinformation about the grade of impurityof used lime and sand. The secondtechnique applied was scanning elec-tron microscopy (SEM), using a JeolJSM-5400. The accompanying energydispersive X-ray analysis (EDX) was per-formed under the SEM equipment usingan Oxford Link analyser with Si (Li)detector and Be window. Due to a smallamount of pigment samples, for theiridentification mostly SEM-EDX was usedand samples were analysed as powderor as cross-sections.RESULTSMortarsThe results showed that in the Slovenemediaeval mural painting several kindsof mortars were used, which can be divi-ded, on the basis of aggregates, intothree principal groups.1. Mortars of lime and sandThe majority of mortars are made bystandard procedure by mixing lime andsand (Knoepfli et al. 1990, Mora et al2001, Kriznar 2006). The compositionmay vary, depending on the quantity oflime and on the cleanliness of the sandused. The elaborated cross-sectionspermitted to observe the calcite matrixand sand grains of different colour,dimension and form (Fig, 1a). The XRDanalysis (Fig. 1b) showed if the mortarscontain mostly calcite (CaCO3) or thereis more quartz. In some samples, dolo-mite, feldspars and some clay minerals,as minor crystalline phases were alsoidentified.If there is more lime than sand in themortar, it is of better quality and moreresistant. When mortars have little limeand are overfilled with sand, the qualityis poorer and a mortar tends to pulveri-(1) Department of Art History, Faculty of Philosophy, University of Ljubljana, A.ker.eva 2, 1000 Ljubljana (Slovenia)(2) Institute of Materials Science (ICMS), Consejo Superior de Investigaciones Científicas (CSIC)-University of Sevilla (US), C/Américo Vespucio 49, 41092 Sevilla, (Spain)palabras clave: Pintura Mural Medieval, Morteros, Pigmentos,XRD, SEM-EDXkey words: Mediaeval Mural Painting, Plasters, Pigments, XRD,SEM-EDXComunicación *corresponding author: pedroji@icmse.csic.esFig. 1a. Selected optical micrograph of a cross-section(x25) of a typical mor tar made of lime and sand. Famlje(1450-60).Fig. 1b. Corresponding XRD diagram for mineralogicalanalysis of powder sample.78Homenaje al Prof. Emilio Galán HuertosMineralogy of Supports and Selected Pigments in Mediaeval Churches of SloveniaComunicaciónse. The sand for the plaster used to betaken from the nearby location, which iswhy the quality of mortar dependsmostly on the geological characteristicsof the territory and not so much on theworkshop itself. However, the grade ofwashing the sand is also important. Thecleanest sand with rounded smallgrains was found in mortars applied inchurches near rivers or lakes.2. Mortars of lime and crushed marble orlime-rockn fewer cases a mortar made of lime andcrushed marble or lime-rock was found.This mortar of high quality is very suitablefor the fresco buono technique (Knoepfliet al. 1990, Mora et al 2001, Brachert2001). In this kind of plasters the presen-ce of calcite has two origins: a) as a bin-der and b) as an aggregate. It has a typi-cal white colour, which can be well obser-ved on cross-sections (Fig. 2a), wherewhite, slightly transparent grains aremixed with white lime. The XRD analyses(Fig. 2b) show the presence of calcite(CaCO3) and some dolomite (CaMg(CO3)2), while in some other cases ofmortars also a small quantity of quartzwas appreciated.It is a kind of mortar that was used inItalian Tre-and Quattrocento for a frescobuono technique, however in Sloveneterritory was mostly related to thosemurals that are stylistically connectedto the North-Alpine regions.3. Mortars with organic additivesOnly in the case of one group of muralpaintings, limited to the north-eastSlovene area of Prekmurje, the resultsshowed the specific construction ofmortars (Kriznar 2006). To the mixtureof lime and sand also organic fibreswere added, in order to improve thequality of the mortar and to give it moresolidity by increasing the mechanicalstrength. The fibres were best observedon the SEM image (Fig. 3).This composition of mortar is unique inSlovene territory and was not found inany other monument of this investigation.PigmentsThe principal mineral pigments appliedwere malaquite (Cu2CO3(OH)2), azurite(Cu3(CO3)2(OH)2) and cinnabar (HgS),identified by EDX on the bases of theircharacteristic chemical elements(Wehlte 1967, Knoepfli et al. 1990,Montagna 1993, West Fitzhugh et al.1987-2007). The first one was veryrarely found and was applied in smalareas like lips or drapery decoration. Itis always related to murals ordered by arich doner, due to its high cost. Whencinnabar is obtained from the mineral, itis considered one of the most expensi-ve pigments. That is why it was soonreplaced by an artificial one, called ver-milion, with the same chemical compo-siton (West Fitzhugh et al 1987-2007).Malaquite was applied more often,however, Slovene mediaeval paintersprefered to use much cheaper, but lesscovering green earth. The most usedpigment obtained from the mineral wasazurite, which can be found on vastareas for sky or vestments of importantfigures, like Virgin Mary. As beeing asemiprecious mineral, the pigment wasunderlayed by gray (veneda) or reddish(morello) colour, in order to use it asless as possible (Knoepfli 1990, Moraet al, 2001).CONCLUSIONSThe research work on selected mediae-val mural paintings confirmed that theprincipal mixture for mortars was themost common one, made of lime andsand. In fewer cases, lime plaster wasapplied, and only in the northeasternregion of Slovenia also organic fiberswere found in the mixture, in order togive more solidity to the plaster.Pigments, made of minerals, were lessused than earths, nevertheless theanalysis identified that cinnabar, mala-chite and especially azurite formed thepalette of painters. Mortars weremostly characterized by XRD, while pig-ments, due to small amount of sample,by SEM-EDX.ACKNOWLEDGEMENTSThe authors acknowledge the financialsupport of Research Project MAT2002-02549, partially financed by FEDER,and the Bilateral Co-operation Projectbetween Slovenia and Spain. The sup-port of CSIC Thematic Network ofCultural Heritage is also acknowledged. REFERENCESBrachert, T. (2001): Lexikon historischerMaltechniken Quellen-Handwerk-Technologie-Alchemie, Callwey Verlag, Manchen.Höfler, J. (1996-2004): Srednjeve.ke freske vSloveniji, Vol. I-IV, Dru.ina, Ljubljana.Knoepfli, A., Emmenegger, O., Koller, M.,Meyer, A. (eds.) (1990): Reclams Handbuchder künstlerischen Techniken, Vol 1-3.Philipp Reclam jun., Stuttgart.Kriznar, A. (2006): Slog in tehnika srednje-veskega stenskega slikarstva naSlovenskem, Filozofska fakulteta Univerze vLjubljani, Zalo.ba ZRC SAZU, Ljubljana.Matteini, M., Moles, A. (1984): Ciencia yRestauración: Método de investigación,IAPH, Nerea, Sevilla.Montanga, G. (1993): I pigmenti,: Prontuarioper l´arte e il restauro, Nardini editore,Firenze.Mora, P., Mora, L., Philipot, P. (2001): Laconservazione delle Pitture Murali, EditriceCompositori, Bologna.Wehlte, K. (1967): Werkstoffe und Technikender Malerei, Otto Maier Verlag, Ravensburg. West Fitzhugh, E., Feller, R., Roy, A., Berrie,B.H. (1987-2007): Ar tist´s pigments, AHandbook of their history and characterisa-tion, (Eds. E. West Fitzhugh, R. Feller, A. Roy,B. H. Berrie.), Vol. 1-4, National Gallery ofAr t: Washington, Oxford UniversityPress:New York, Oxford.Fig. 2a. Cross-section (x25) of a mor tar made of limeand crushed lime-rock or marble. Selo near Zirovnica(around 1430).Fig. 3. SEM image of an organic fibre on the sur face ofthe mor tar sample from Mar tjanci (x200).Fig. 2b. Corresponding XRD diagram. for mineralogicalanalysis of powder sample.

Mineralogy of supports and selected pigments in mediaeval churches of Slovenia

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Mineralogy of supports and selected pigments in mediaeval churches of Slovenia

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idUS. Depósito de Investigación Universidad de Sevilla