Figure 1 General view of the square shaped apse of the church of S. Andrea.

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1 1655 THE MURAL PAINTINGS OF S. ANDREA IN MELZO (ITALY): ANALYTICAL INVESTIGATION OF THE PIGMENTED LAYERS. TONIOLO, l. CNR Centro "Gino Bozza" Milan (Italy) CARIATI, F., POLESELLO, S. Dip. Chimica lnorg. Metallorg. e Analitica, Universita degli Studi di Milano (Italy) POZZI, A. lstituto di Scienze Mat. Fis. e Chimiche, Universita degli Studi di Milano, Sede di Como (Italy) SUMMARY The mural paintings of the church of S. Andrea in Melzo, Milan (Italy) have been investigated during a recent conservation work. The identification of the employed pigments has been carried out by reflectance micro-ftir spectrophotometry and X-ray spectrometry, analysinig the same polished cross-sections. These analytical techniques allowed to distinguish different situations of the pictorial layers and pointed out some interesting features of the green and blue pigments (green earth, malachite, azurite). Moreover these microscopic techniques allow the localization and identification of the employed materials on the basis of chemical results. The application of FTIR spectrophotometry also provides some informations about the presence of organic compounds used as pigment binder or fixative. 1. INTRODUCTION The church of S. Andrea in Melzo (Milan, Italy) was surely built before 1245, year in which a first important document refers about its existence. At the beginning of this century the church was deconsecrated and the internal walls covered with a common pale yellow plaster. Few years ago the mural paintings that decorate the square shaped apse were discovered and the "Virgin in throne" and the "Martyrdom of S: Andrea", ascribed to the Leonard's school. This paper deals with the analysis of the pictorial layers of these mural paintings, carried out on the occasion of the recent conservation work. The sampling concerned mainly the Martyrdom of S. Andrea (Fig. 1) and only few samples come from the other paintings of the apse. The aim of the work is to identify the different employed pigments applying two very powerful analytical techniques - reflectance micro-ftir spectrophotometry and X-ray spectrometry (EDAX) - carried out on the same polished cross sections. Figure 1 General view of the square shaped apse of the church of S. Andrea.

2 EXPERIMENTAL 2.1 Sampling The sampling was carried out according to the indications of the Normal Reccomandation (1); microfragments of the painted layer were collected with the scalpel only. Samples are described in Table Reflectance micro-ftir spectrophotometry (Micro-FTIR) Polished cross sections were examined between cm-1 using a JASCO WS-IR100 infrared spectrophotometer equipped with a MCT detector and an Olympus optical microscope. Specular reflectance spectra were converted to transmission spectra performing the Kramers-Kronig integration by the suitable software Energy dispersive X-ray spectrometry (EDAX) Scanning electron microscopic observations were carried out on a Jeol C35 microscope and the EDX analyses performed with a Link spectrometer. The polished cross sections were covered with a graphite conductive film. Sample Location Color 50 child back skin pale brown 51A child shoulder skin pale brown 51 child cloth pale grey blue 53 child arm skin pink 54 face of the child in the center pink 55 left foot of S.Andrea dark pink 56 left leg of S.Andrea dark pink 57 torax of S. Andrea pink 58 background country, upper left part of the painting green 62 cloth of a human figure under the foot of S.Andrea yellow 63 Moor turban green 66 hair of the woman with the yellow cloth gold yellow 68 Moor face skin brown 69 cloth of a standing human figure yellow 71 sash of the dress of a woman pink 72 Moor cloth green 76 sky behind the Virgin in throne blue Table 1. Samples collected from the mural paintings of the apse. Locations and colors. 3. RES UL TS AND DISCUSSION 3.1 The "pink" pigments All the samples coming from the skin of human figures showed approximately the same composition based on the mixture of an ochre pigment with calcium carbonate. The ochre pigments have been identified comparing the micro FTIR and the EDX spectra; the elemental composition of the pictorial layers - Mg, Al, Si, Cl, K, Ca and Fe, - corresponds clearly to the silicate FTIR pattern showed in Fig. 2.

3 1657 ll0..:1\.1 ~ ~ K...-~. 5 I rl - ~ ~---'---'---'---'---''---'----L- J..L.;L, J. L J UJ1J.'./i:-n1.1.r11b i: :r: Figure 2 FTIR spectrum of a pink sample: the silicate pattern of an ochre pigment is evident. The slight spectral differences among the different examined samples are difficult to interpretate. Only the optical observations and the real microscopic color of the crystals allows to distinguish between the red and yellow ochre. The spectrum showed in Fig.2 is obtained from a red ochre layer (1136, 1068 cm- 1 ) characterized by a high hematite content. The sample 71, showed interesting red particles in the pigmented layer: EDX analysis of a single crystal, pointed out the presence of vennilion (red mercuric sulfide, HgS - cinnabar) so that the particular pink hue of the sample was achieved with a little amount of this pigment (2). No absorption peak due to this mineral can be evidenced in the mid-ir. There are three kinds of mercuric sulfide pigment: the natural mineral form, which is simply finely ground cinnabar; two synthetic forms, prepared with different methodologies from the native cinnabar (2). The examination of the polished cross section doesn't allow to distinguish what kind of vermilion was used in the painting. 3.2 The "green" pigments The green samples showed the employ of two different green pigments. The first identified pigment is green earth, a wide used green pigment which is an allumino-silicate (calcidonite and glauconite) (3) showing a very reproducible silicate FTIR pattern (Fig. 3: 1122, 1082 and 1059 cm- 1 ). The corresponding EDX spectrum shows a very high content of S (Fig. 4 EDX p.86) indicating that the green pigment has been applied on a gypsum ground. This is particularly evident also from the FTIR spectrum (Fig. 3-A) in which the gypsum prevails over the pigment. This sample, coming from the Moor cloth, may be ascribed to a repainting; the same pigment - green earth - is, actually, employed for the background country (Fig. 3-B) applied with a true fresco technique on the lime plaster. tot. ~.. :. ~ i B - f. t A

4 1658 Finally, the Moor turban is painted with malachite. FTIR reflectance spectra of large crystals (Fig. 5) evidenced the presence of this high value pigment. The significant spectra obtained after K/K conversion are easily comparable with the transmission spectra available in literature (4). The attribution of the observed spectra to the malachite is confirmed by EDX analysis which detect only Cu after Ca and S in the pigmented layer. The malachite is a very stable pigment in a strong basic environment so that it should have been applied directly on the lime plaster; sulfur belongs to the surface gypsum layer, thus being a decay product. X-RAY: 0-10 k ev ILive: 200s Preset: 200s Rema i ning:.real: 23'ts 15% Dead f ,,, Os Figure 4 EDX spectrum of the green sample coming from the Moor cloth: green earth painted on a gypsum ground 103. f :.: ~ ~ I ~ - J 51. ;:.::; ~_... _,, J.. J... J..L.. J L_J 200~ '.:,(H). ~l 1 ~) i:n:1 ~ 0 7C:0. ).j IJ.l1J.'v'E''i11J:li1bi: r Figure 5 FTIR spectrum of a single crystal of malachite coming from the Moor turban. 3.3 The "blue" pigments Azurite has been evidenced in the samples coming from the sky behind the Virgin. A very characteristic spectrum (Fig.SA) is obtained only from the analysis of a single crystal favoring the specular reflection component (5).

5 1659 On the contrary, analysing the whole pigmented layer only gypsum and calcium carbonate are pointed out (Fig.68) and no informations about the pigment are obtained. The presence of azurite has been confirmed by EDX analysis (Fig. 7 p.131) that showed Cu, Ca and s in a large amount. In conclusion, the pigment should have been applied on a gypsum ground, considering that, in the lime environment, it would have been transformed into the green basic copper carbonate. ~0:3. ~:, , A Y,, 2 l }. 6 ) '----'--'----'--'----'--'----'--'-4-'--'---'--'----'---' ~0.0 1~ \JJi:1.v~ n1.1.mbe1 Figure 6 FTIR spectrum of azurite coming from the sky behind the Virgin. A) single crystal; B) spectrum of the whole pigmented layer. X-F:ft'-r' : 0-10 k o<ij Liv~: 200 ::: Pre s ~ t : 20 (1 s Rem.> in in ~: 0 s Re.> \: 223s 10% Oe.>d Figure 7 EDX spectrum of the whole azurite layer. The pale grey blue color of the cloth that wraps a little child in the lower part of the painting, is obtained by a mixture of very finely ground vegetal carbon and lime powder. In fact, the EDX spectrum allowed to detect only Ca, Mg and Si in trace. The morphology of the black particles is not significant because of the polishing treatment of the sample; nevertheless the absence of P allows to exclude the employ of bone black (6). Carbon powder of vegetal origin is the more usual black pigment employed to tone down the colors (7, 8). The FTIR reflection spectrum, beyond the calcite peaks, pointed out the presence of an organic

6 1660 component in the lime mixture (Fig. 8). Because of the general low reflection power of the organic material and the interferences of the inorganic matrix, it is very difficult to identify the organic binder from the FTIR spectra only and no conclusions may be drawn about the organic binder that was added to this mixture. Micro-FTIR analysis should be considered only a screening method: to identify organic compounds, more specific and sensitive analyses (GC-MS, HPLC) should be perfonned (9). The examined painted layer is, actually, a 'tempera' in the widest meaning of the word (6). 1a0.00 ~ ,,----, / \ -.~ \ l.i \ J. I (':_ \ i L! ': I \,...,I j I~ 1. I.! '' ~'\_/'(~ ' I 4.!. ~j,\' ~---'----'-----''----'----'----''-----'----'-~-~-~~-~ l50(j. ;J bkt vi:r1l~ l,b e r Figure 8 FTIR spectrum of the pale grey-blue sample. Beyond the calcite peaks it is evident the presence of some organic compound The uye/low" pigments The EDX spectra obtained from the yellow samples indicate the employ of yellow ochres. This kind of pigments are composed by clay minerals that contain iron hydroxide minerals (yellow) and different amount of manganese oxide. The natural yellow ochre (natural earth) are generally clear and transparent and are darkened by suitable calcination procedures to obtain the burnt earth (being characterized by high amount of Fe and Mn oxides) (4). The FTIR spectra of these samples are not so meaningful for what concerns the pigment; only silicate peaks are evidenced as reported above for the pink samples. 3.5 The "violet" pigments The sky and the clouds of the upper part of the painting are violet. The used pigment is the so called "smalt" obtained grinding a cobalt containing glass (10). The EDX spectrum of some blue crystal of the colored layer, shows the characteristic composition of the above mentioned pigment: Si, K, Fe and Co (Fig. 9 pag.122). :x:-f;fi'/: o - 10 l'., 1 J Li";-:.: 20(1 ~ Pr~;;.:.:~~ : 200:; F~ ~ ma.. in i n ~ = (I::: R~a. l: 232:; 1 '7 ;~ D ~c.d - Figure 9 EDX spectrum of a blue crystal coming from the violet clouds sample.

7 _/ 1661 The violet color is obtained adding to the blue powder a red pigment, most probably hematite, as it is confirmed by the presence of a high amount of iron in the EDX spectrum of the whole pigmented layer. In this case, a significant micro-ftir reflectance spectrum of the pigment was not obtained; the collected FTIR spectra of the painted layer indicate only the presence of some silicate compound together with the calcite. Moreover, because of the optical characteristics of the FTIR microscope, the blue pigment particles are too small to obtain a reflectance spectrum of the smalt. 4. CONCLUSIONS The applied microscopic techniques allowed to detect precisely the employed pigments and indicate the presence of some organic binders. A very interesting advantage of the reflectance FTIR technique is that it doesn't need a particular handling of the samples and may be carried out on the same stratigraphic section prepared for the SEM examination. Actually, the chemical investigations carried out together with the traditional optical microscopy (11) are all destructive techniques (XRF, XRD transmission FTIR) that requires some mg of powder. The upper part of the "Martyrdom of S. Andrea" is painted with a true fresco technique and it is in a quite good state of conservation; nevertheless, the employ of "smalt" for the clouds allows to indicate the late XVI century, as the possible date in which it has been accomplished. The use of smalt as a blue pigment, coming from the venetian region, was introduced in Lombardy only at the end of XVI century (12). The state of conservation of the group of figures under the Martyrdom Cross is rather bad; in spite of the valuable pigments employed (malachite, vermilion ecc.), large areas have been painted with a 'tempera' technique and most painted surface is lost. On the contrary, the sky, behind the Virgin in throne, is painted with azurite on a gypsum ground and is, nowadays, well conserved. REFERENCES 1. Raccomandazione Normal 3/80 "Campionamento", Ed. ICR-CNR, Roma Gettens, R.L. Feller, W.T. Chase "Vermilion and Cinnabar" in Mists' Pigments A.Roy ed., vol II, Washington Grissom "Green Earth", in Artists' Pigments (R. L. Feller ed.) vol I, Washington Gettens, and E. West Fitzhugh, "Malachite and Green Verditer", in Artists' Pigments (A. Roy ed.) vol II, Washington Gettens, and E. West Fitzhugh, "Azurite and Blue Verditer", in Mists' Pigments A.Roy ed., vol 11, Washington R.J.Gettens, G.L. Stout "Painting materials" Dover Pub. Inc., New York, J.Winter, HThe characterization of pigments based on carbon", Studies in Conservation. 28, 1983, pp White "Brown and black organic glazes, pigments and paints", National Gallery Technical Bulletin 10, 1986, pp Nowik "Acides amines et acides gras sur une meme chromatogramme - Un autre regard sur!'analyse de liants en peinture" Studies in Conservation 40, 1995, pp Muhlethaler, J. Thissen "Smalt" in Artists' Pigments A.Roy ed., vol II, Washington Parrini, G. Pizzigoni, s. Sfrecola Pigmenti, colori e problemi ottici degli affreschi" in. La Cappella Brancacci. La scienza per Masaccio, Masolino e Filippino Lippi, Ed.Olivetti 1992 pp Montagna "I pigmenti. Prontuario per l'arte e ii restauro", Nardini Ed., Firenze, 1993.