Colour and composition of nodules from the Calabrian ?· Colour and composition of nodules from the…

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  • ABstrACt - Pliocene clays in rocca imperiale(north Calabria - italy) and monasterace (southCalabria- italy) have oxide and hydroxide iron nodulesof a range of colours, varying from brown to red. it islikely that the inhabitants of some colonies in magnaGraecia (who already used the clay deposits toproduce bricks) had detected the presence of theabove-mentioned raw materials and decided to usethem to produce mineral pigments and to decoratepolychrome artefacts. the nodules were pulverizedand analysed through sEm-EDs, XrPD andcolorimetric analysis; further, they were heated at275C, 400C, 550C e 750C, monitoring theirmineralogical and chromatic transformations. ourstudy pointed out that it is possible to chemicallydifferentiate the nodules of monasterace from thenodules of rocca imperiale. Furthermore, our studyproved that it is possible to produce mineral pigmentsby using such raw materials.

    riAssunto - le argille Plioceniche di roccaimperiale (nord Calabria - italy) e monasterace (sudCalabria- italy), contengono noduli di ossidi eidrossidi di ferro di colore variabile dal marrone alrosso. molto probabile che gli abitanti di alcunecolonie della magna Grecia, le quali gi utilizzavanogli stessi depositi argillosi per la produzione di laterizi,

    avessero notato la presenza di queste materie prime ele avessero utilizzate per la produzione di pigmentiminerali, impiegandoli per decorare manufattipolicromi. i noduli sono stati polverizzati e studiatiattraverso analisi sEm-EDs, XrPD e colorimetriche;inoltre, sono stati riscaldati alle temperature di 275C,400C, 550C e 750C, monitorando le trasformazionimineralogiche e cromatiche. lo studio ha evidenziatoche possibile differenziare chimicamente i noduli dimonasterace da quelli di rocca imperiale e ha dimo -strato che possibile produrre pigmenti mineraliusando queste materie prime.

    KEy WorDs: Ochres; Iron oxides; Iron hydroxides;Kaulon; Monasterace; Rocca Imperiale; Greek

    colonies; Policoro; Amendolara.

    introDuCtion

    since prehistory, man has always tried toexpress himself through art forms, in someinstances using mineral pigments extracted fromnatural deposits with a high content of ironhydroxide and oxide (marean et al., 2007; iriarteet al., 2009), commonly known as ochres (fromthe Greek word ochrs = yellow). the ochre

    PerIodICo di MIneraloGIaestablished in 1930

    Period. Mineral. (2010), Special Issue, 59-69 doi: 10.2451/2010Pm0021http://go.to/permin

    An International Journal of

    MINERALOGY, CRYSTALLOGRAPHY, GEOCHEMISTRY,

    ORE DEPOSITS, PETROLOGY, VOLCANOLOGY

    and applied topics on Environment, Archeometry and Cultural Heritage

    Colour and composition of nodules from the Calabrian clay deposits: apossible raw material for pigments production in Magna Graecia

    DomEniCo miriEllo1*, AnDrEA BloisE1, AnnA mAriA DE FrAnCEsCo1, Gino miroClE CrisCi1,FrAnCEsCo ChiArAvAlloti2, DonAtEllA BArCA1, mAuro FrAnCEsCo lA russA1 and ElisA mArAsCo1

    1Dipartimento di scienze della terra, universit degli studi della Calabria,Ponte P. Bucci cubo 12B, 87036 Arcavacata di rende (Cs), italy

    2C.n.r - irPi istituto di ricerca per la Protezione idrogeologica, via Cavour, 87036 rende (Cs), italy

    Submitted, September 2010 - Accepted, November 2010

    * Corresponding author, E-mail: miriello@unical.it

    miriello:periodico 30/11/2010 15:32 Pagina 59

  • 60 D. miriEllo, A. BloisE, A.m. DE FrAnCEsCo, G.m. CrisCi, F. ChiArAvAlloti et al.

    owes its pigmenting capacity to various ironcomposites, which determine its variety ofcolorations (red, yellow, orange, brown andgreen).

    Generally ochres contain more than 10-12 %of iron oxides. the percentage of Fe2o3 rangesbetween approximately 10 and 20 % up to morethan 90 % in the deep red ochres (Benbow,1989).

    As centuries went by, man learnt how totransform such raw materials improving theiraesthetic features, thus obtaining mineralpigments of various colours. Around 2000 B.C.,man realised that a range of browns and redscould be obtained by calcining raw ochres in air

    (Cornell and schwertmann, 1996). Probably theGreek populations that settled in the magnaGraecia (Arena, 1996) - south of italy - betweenviii and vii century B.C. were also aware ofthis. in magna Graecia, art expressed itselfthrough the realisation of numerous polychromeartefacts, making a wide use of mineral pigmentsto decorate plasters, pottery and other handmadeobjects. vitruvius talks about the use of naturalearth pigments in Greek art in his book vii ofDe Architectura (vitruvius, 1990). he pointsout that, in Athens, when an ochre vein wasfound in the silver quarry, it was followed andextracted as if it were a precious raw material.

    in particular, many artefacts, decorated with

    Fig. 1 - a) semplified geological map of monasterace area (by De Francesco et al., 2009 modified); b) image of monaste-race nodules in clay sediments; c) studied samples (mo= monasterace, ri = roccaa imperiale); d) semplified geologicalmap of rocca imperiale area - by miriello and Crisci, 2006 modified; e) location of some Greek archeological sites nearrocca imperiale.

    miriello:periodico 30/11/2010 15:32 Pagina 60

  • mineral pigments, were found, during excavations,in the archaeological area of the ancient Greekcolony called Kaulon, located in Calabria - southof italy - on the ionian coast, near the village ofmonasterace marina (Fig. 1a). Among thefindings above, we may mention architectonicearthenware dating back to v century B.C.(Greco, 1996; raco, 2000) relating to a roof ofthe colle di Passoleria, where we findrepresentations of leonine heads decorated withpigments of various colours-black, brown andred (Fig. 2). looking at these beautiful works ofart, many archaeometric questions and scientificissues arise. the present study will attempt to

    shed new light on some of these questions and,in particular if raw materials potential source ofmineral pigments could be locally found. thesame pigments will be reproduced in laboratoryand the mineralogical transformations as well aschromatic alterations taking place during theheating process will be monitored.

    sAmPlinG oF thE noDulEs

    literature only mentions few Calabrian areaswhere ochre quarries exist. some historicalquarries have been signalled in Pazzano, avillage in the province of reggio Calabria

    61Colour and composition of nodules from the Calabrian clay deposits: a possible raw material for ...

    Fig. 2 - Decorated heads of lion (v sec. B.C.) discovered on the Colle della Passoliera at monasterace - Calabria, italy(monasterace museum).

    miriello:periodico 30/11/2010 15:32 Pagina 61

  • (scarzella and natale, 1989) and in the Grottadella monaca, a karstic cave located in thevillage of santAgata dEsaro in the province ofCosenza (Dimuccio et al., 2005). however, in anarea few kilometers away from Kaulon, wefound outcrops of Pliocene clay sediments (Fig.1a) of the monte narbone Formation (Cavazzaet al., 1997). the clay sediments closer to thearchaelogical site of Kaulon are generallyaffected by moderate agricultural activities. onthe contrary, the clay sediments foundapproximately 3.5 kilometres north-West fromthe archaeological area have a lower degree ofanthropisation, which allowed us to detectnumerous, centimetric size, brown nodules (Fig.1b and 1c). some of these (samples mo4, mo9,mo10.3) were easily sampled on the surface ofthe clay sediments. the location of the sampledarea is shown in Fig. 1a. the nodules have acoarse sand aspect (Wentworth, 1922) and someof them crumble easily producing a brownish/reddish powder. it is likely that their aspect,which is very similar to the one of typical ochres,attracted the attention of Greek colonists, whohad already used the same kind of clay toproduce bricks (De Francesco et al., 2009); andit is also likely that they used the nodules for theproduction of mineral pigments.

    Brown nodules, similar to the ones samplednear the village of monasterace, were detectedin the village of rocca imperiale, in the provinceof Cosenza (Fig. 1d). Also in rocca imperialethe nodules are easily found in Plio-Pleistoceneclay sediments (Fig. 1c and 1d) on top of therocca imperiale thrust (ogniben, 1969;Ghezzi, 1973; Cucci and Cinti, 1998). some ofthese nodules (samples ri1, ri9, ri10) weresampled by the area shown in Fig. 1d. Plio-Pleistocene clay of rocca imperiale was usedduring the middle Age to produce bricks(miriello and Crisci, 2007) and we may assumethat also Greek colonists of the close areas ofAmendolara and Policoro (Fig. 1e) used thenodules to produce pigments.

    our research does not aim to study thegeological genesis of monasterace and roccaimperiale nodules, but it aims to prove that theycan be used to produce mineral pigments,starting from the study of their chemicalcomposition and mineralogical and colorimetricchanges that take place during the heatingprocess in air. however, iron-manganese nodulesand concretions may form in soils after reductionand subsequent oxidation of Fe and mn, as aresult of seasonal changes in soil moisture (liuet al., 2002; scarciglia et al., 2003). underreducing conditions, Fe and mn release Fe(ii)and mn(ii) ions to the soil solution. When thesoil dries out, Fe(ii) and mn(ii) oxidize andprecipitate, forming new metal oxides.

    the present study may be considered as apreliminary phase of a future research, whichwill be carried out on a higher number ofnodules.

    EXPErimEntAl AnD AnAlytiCAl mEthoDs

    Each nodule was pulverised in an agata mortarand heated in air at a controlled temperatures(275C, 400C, 550C and 750C) for 8 hours.

    major chemical composition of the naturalnodules was performed by sEm-EDs (scanningElectron microscopy with Energy Dispersive X-ray spectroscopy) on pressed pellets, whichwere representative of the powder bulk sample(tABlE 1).

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