- / 1663

MURAL PAINTING IN SAN TARASIO CHAPEL IN THE CHURCH OF SAN ZACCARIA, VENICE: A STUDY OF THE STATE OF CONSERVATION OF PAINT FILM

FASSINA, V., ROSSETTI, M., Soprintendenza ai Beni Artistici e Storici di Venezia ZUCCHETTA,E. Soprintendenza ai Beni Ambientali e Architettonici di Venezia

SUMMARY In this paper some preliminary results on the state of conservation of mural painting and gilding, are presented. At the moment the restoration work is currently in progress. In order to obtain significative results the following analytical methodologies were used: - Observations of cross sections by using reflected and UV light microscopy, improved by chemical micro tests showing qualitatively the presence of organic compounds. - Observations by Scanning Electron Microscopy (SEM) improved by microprobe Energy Dispersive Spectrometer analysis (EDS). - Ion Chromatography analysis of water soluble anions. First of all the pigments forming the colour layers were characterised. As regards the paint film it presented some different state of conservation: in fact in some areas, surface appeared very bright, and in other one it showed a whitening effect. The whitening and brightening effects could be ascribed to previous treatments carried out in different time in the past. During the current restoration work some problems of cleaning were met due to the difficulty to remove the treatment substance without damaging the paint film. According to our hypothesis the substance used during the most recent restoration intervention, probably interact with the paint film so causing a difficulty to remove decay products generated by this interaction without damaging paint film. In other areas there are gilding with different feature: the results of analysis showed two kind of gilding, one containing a gold lamina and another one with tin and gold. The latter was found in different areas. Gypsum due to sulphation of calcite is sometimes present on red scialbatura of bricks and on painted surface

2. HISTORICAL BACKGROUND AND INTRODUCTION The frescoes in the Chapel of San Tarasio, formerly the apse of the old Church of San Zaccaria, constitute one of those fortunate instances where the artist (or in this case two artists) actually signed the work in question, so attribution poses no problem. The frescoes, depicting St. John the Baptist, the four Evangelists, Luke, Mark, John and Matthew, St. Zacharias and God the Father, bear the names of Andrea da Firenze (identified by Fiacco in 1920 as Andrea del Castagna) and an assistant, a certain Francesco da Faenza; the inscription also gives the date as August 1442. The very fact that two artists were involved, however, raises the thorny problem of identification of their separate contributions, though there can be no doubt that the organic and harmonious nature of the whole means that the overall design must be the work of Andrea, while Francesco da Faenza, whose name also appears below that of Andrea, will have been responsible for translating at least some of his more famous companion's drawings into their final form. One way of distinguishing between the two artists' work might be to attribute to Francesco da Faenza the less accomplished parts of the cycle: some of the less assured winged putti on the intrados of the arch framing the apse, for example, though these too have something definitely Castagnesque about them. Fiocco's attribution of the minor sections of the San Zaccaria frescoes to the mosaicist Silvestro, known to have executed the two mosaic depictions of St. Anthony Abbot and St. Vincent Ferrer in the right transept of St. Mark's Basilica in 1458, now seems less than convincing. It is more logical to think of Francesco da Faenza as responsible for the figure of St. Mark, the painting of which betrays a certain immaturity and superficiality, while Andrea must have painted God the Father, crowned and seated among clouds, his hand raised in blessing; the breadth of the head is typical of 1664

Andrea's later work, and the solemn expression on the face seems clearly to derive from Byzantine depictions of Christ Pantocrator. The three red-winged cherubs at the top of the mandorla are certainly by Andrea, while the other three, lower down among the clouds, are by a less expert hand, pemaps that of Francesco da Faenza. The St. John the Evangelist, however, constitutes a real problem of attribution since it is painted quite differently from the other figures with the shot effect of their garments and the plastic vigour achieved through contrasts of light and colour. The figure is infused with colour and bathed in daylight almost redolent of ; the stance is meditative and the Saint has a red book under his arm: in view of these characteristics, most critics are of the opinion that it was painted by . Formal considerations again prevail over chromatic values in some of the figures in the intrados of the arch, but they are not sustained by the almost atmospheric effect discernible in the St. John. The San Tarasio St. Luke may have engaged both Francesco and Andrea, a certain angularity in the folds of the cloak being traceable to the latter, while the forced realism in the figure's fixed gaze and the awkwardness of the arm both suggest the hand of Francesco. St. Zacharias can safely be attributed to Andrea, the severe facial expression suggesting the influence of Cimabue and of Donatello's statues of prophets in the campanile of the Duomo in Florence. In the last two segments of the fresco, on the right, Francesco probably painted the scrolls and Andrea the two seraphs. On the intrados of the arch, ten winged putti, painted in various attitudes, support the weight of ten tondi containing busts of prophets and saints. We may reasonably suppose that Andrea had accepted a commission to decorate not only the apse but also the ceiling and walls of the presbytery (apart from the side niches, the San Zaccaria chapel is similar to the Ovetari Chapel at the Church of the Eremitani in Padua), probably with a series of stories of St Zacharias and St. John the Baptist, from Gabriel's announcement to the prophet of John's birth, through various episodes in the saint's life to his death and burial, with the four panels of the cross vault would probably have been frescoed with depictions of the Doctors of the Church. We can only surmise such a development, however, because for some reason Andrea's scheduled work in Venice was interrupted and the city's only examples of his tormented and rugged art are the frescoes in the apse of the chapel.

Previous restorations

Andrea del Castagno's frescoes have been the subject of conservation work at least since the middle of the XIX Century. Research is still going on at the Venetian State Archives into the precise nature of the work done around 1850, but it is already clear that damp and inadequate maintenance. as usual in Venice, were the main causes of the frescoes' extremely poor condition at the time. Attempts were made to consolidate the frescoed panels and ribs of the apse using repeated applications of beverone di caseina and emulsified oils to fix the paint. The restorers also carried out a certain amount of repainting and retouching, especially on the blue background. Renewed attempts to consolidate the paint were probably made later using other fixatives and varnishes. In 1893, Pietro Paoletti reported the fall of a section of fresco three years before and in 1915 Laudedeo Testi confirmed the continuing poor state of what he described as Andrea da Murano's work as "much blackened, crumbling and generally in very bad condition". Not long after, in 1923, Carlo Gamba , writing in "Dedalo" about "a previously unrecognised work by Andrea del Castagna", complained that further restoration of the paintings was still not finished. We have no documentation of the work carried out in the 1920s, but it evidently failed to stabilize the condition of the frescoes if in 1949 Muraro writes that they once again required radical attention. A few years later, in 1955, they were still in appalling condition but now that their high quality was recognized (in 1920 a layer of whitewash was removed to reveal the cartouche containing the name "Andreas de Floretia", whom Fiacco identified as Andrea del Castagna) Mario Salmi urged yet another restoration, directed mainly at cleaning what was described as the "extremely darkened" 1665 surface. Salmi's recommendations were promptly acted upon by the then Superintendent for Monuments of the Veneto, Antonio Rusconi. At the time, before work started, it seemed apparent that no lasting results could be achieved if the conservation operations had once again to be carried out in situ. M. Muraro, then an Inspector for the Superintendency, was in favour of radical action rather than the constant "drip" of partial efforts which brought only temporary solutions. Muraro's attitude was by no means innovative, however, for as long ago as 1863 Cavalcaselle had proposed similar vigorous action, otherwise the tremendous damage arising from the damp would certainly result in "the loss of the paintingsj. All the arguments were put to the Supreme Council for Antiquities and Fine Arts, appointed by the Ministry to decide exactly what should be done. Fortunately, it was decided to reject Muraro's suggestion that the frescoes should be detached, a conservation technique which was much more freely used in those days than is now believed to be necessary or wise; instead, the Council adopted the more reasonable proposal of another in situ restoration. Work was carried out by Leonetto Tintori of Prato and Alfio del Serra under the supervision of the Supreme Council itself and was completed in October 1956. Their action consisted principally in the removal of efflorescences of calcium carbonate and mould from the surface, and in the fixing of paint which photographs taken with raked light had shown to be flaking off or crumbling. Plaster in danger of falling was reattached to its support and the original blue of the backgrounds was restored by removing superimposed layers of casein, oil, shellac and the other fixatives used in previous restorations. Sections where colour had been lost were painted in with neutral colours, avoiding disturbing clashes with surrounding areas, in an attempt to give a stable appearance to the painted surface. The problem of damp, however, remained the main enemy of the paintings and the threat that had prompted Muraro to prefer their detachment to the brief respite afforded by the usual treatment. The Supreme Council therefore proposed a series of as it were "passive" measures designed to reduce the high degree of humidity; these included the rejection of proposals to place windows or holes in the roof, for fear that this might alter the delicate hygrometric balance originally established in the space between the vault and the roof tiles. They also suggested closing the access to the crypt, which was almost always flooded (to stop humidity building up in the crypt itself they proposed a ventilation window in the outside wall). The chapel was to be aerated by opening the lower sections of the apse windows rather than the upper sections, which were judged too close to the paintings. Despite these efforts the frescoes were again in danger by 1970, when the Central Restoration Institute of took direct action after all the windows and roof of the chapel had been repaired (rainwater had been leaking in through the roof and broken guttering had resulted in rainwater pouring onto the wall and seriously damaging the paint film). There were some miniscule losses of paint, for example in the cloak of the St. Luke and in limited areas of gilding, but these too were not considered to be worrying, probably being caused by earlier saline efflorescences; these are now reduced to a minimum. Some substantial cement-filled holes, for example in the St. Zacharias and where a tie rod was inserted into the arch framing the apse (incidentally causing considerable damage to the frescoes) are documented and date from 1906-07. On the occasion of restoration work in progress it was necessary to carry out some analyses to know the nature of materials and the state of conservation of the fresco. There are some problems concerning the presence of dark patina on pictorial film and some brightning of the surface localised in some areas. Sometimes the presence of saline efflorescence give a whitening effect. In the first phase of cleaning, there were some difficulty to remove from the surface the old treatments without damaging the paint film.The gildings showed different aspects such as brightning or grey patina. 1666

3. MATERIALS AND METHODS

The samples are divided in different groups dealing with: samples of fresco, of gilding, of brick and samples chosen to identify organic compounds. In order to obtain significant results the following analytical methodologies were used: - Observations of cross section .using reflected and UV light microscopy, improved by chemical organic spot tests. - Observations using scanning electron microscopy with microanalysis EDS. - Ion chromatography to identify and quantify the anions of soluble salts. - Infrared spectrometry to identify organic compounds, in particular old treatments.

4. DISCUSSION OF THE RESULTS a) Observations with reflected light microscopy and with scanning electron microscope of samples of fresco paint film

The initial stage of the study dealt with the characterisation of the constituent materials of the mural painting and with the determination of pictorial technique. The sampling was made on the different kinds of pigments and on visible retouchings. In order to check the homogeneity of the sky painting, some samples were taken from different areas of the sky. Other samples were taken from different subjects and in particular from backgrounds, which are generally retouched. Two types of pictorial film and false brick can be observed: i) The first type is related to samples, in particular those coming from the sky, and is characterized by several coloured layers on intonaco that shows porphyric structure and is composed of calcium carbonate with calcite, quartz and dolomite crystals. These samples feature a preparatory layer composed of calcium carbonate and carbon black; in following layers there are azurite, red ochre and permanent white in calcium carbonate medium. Sometimes the azurite shows a different intensity of tone, caused by different degree of grinding. Sometimes smaller crystals are altered: for example copper salts and malachite are present, both due to transformation of azurite. ii) The second type is characterized by samples in which, as well as intonaco,we find one coloured layer containing such pigments as red ochre, yellow ochre, burnt Sienna, black carbon, green earth, cinnabar and permanent white, the latter in small quantities only on the surface. In all these samples traditional pigments, characteristic of the fresco tecnique. have been employed. Some spot tests were carried out to identify the presence of proteins and fats, because as archive documents show, there have been several restorations over the last century. These tests gave a negative results. Sometimes, a dark thin protective film occurs on the surface, it is possible that this is connected with a treatment, probably the last, carried out in 1970. iii) False brick is used to highlight architectural structures such ogive arches and vaulting ribs. It is very probable that these parts were retouched during several interventions, in particular over last century. With regard to false brick, some remaking are evident. Intact in the original elements we find the intonaco covered by one or more layers. Sometimes remaking composed of a single thick layer of gypsum are present, perhaps a stuccatura to cover the fall of superficial coloured layers. b) Observations with reflected light microscopy and with scanning electron microscope of samples of gilding

In this group of samples two different kinds of gilding techniques have been found : i) The first type is related to samples, coming from the aureoles of the saints and from decoration as light rays, and it presents a dark superficial patina and a considerable thickness that gives an evident increase of relief; today this kind of gilding is no longer very bright. _/ 1667

Generally the samples include a preparatory layer composed of oil mordant added to yellow or brown pigments such ochre and earths. Sometimes particles of pigments, from the layer underneath, are visible, for example black carbon or azurite. Then one tin lamina covered by gold lamina. Rarely the presence of two tin laminae is rarely visible; both are covered by gold lamina. This may be casual in origin, for example an overlap of metallic leaf, rather than a retouching . A grey-coloured layer is recurrent on the surface, this is composed of gypsum but there is also an organic compound that cannot be identified by EDS microanalysis. This one is certainly connected with a treatment. ii) The second type of gilding, taken from the cherubs, is very bright compared to the previous one. In this case there is only gold lamina on oil mordant mixed with red ochre, directly on the fresco surface. Also in this case a grey protective film is present with small quantities of gypsum connected with processes of sulphation of calcite, probably existing before this treatment. Spot tests to identify fats were positive in correpondence of the oil mordant layer.

c) Observations with reflected light microscopy and with the scanning electron microscope of samples of false brick

Generally these samples are characterized by the presence of white-coloured intonaco, at the bottom, composed of calcium carbonate. In some samples, such 5 and 7, the layers comprise calcium carbonate, black carbon, yellow ochre, red ochre and cinnabar, the latter only in the surface. Spot tests for fats are positive only in sample 5, with respect to a discontinuous brown-coloured layer, that shows a light yellow fluorescence, in UV light, connected with the presence of oil. In other samples some layers composed alternatively of calcium carbonate and ground brick were observed. In the sample coming from black background in the upper part, a black carbon layer is visible. In another case, there are layers composed of gypsum as plastering. It is possible that this is a repair because the technique is different from other samples. probably where retouchings are made.

d) Preliminary investigations using infrared spectometry to identify organic compounds

To determine the compounds that produce the whitening and shining effects Some preliminary analyses were carried out . These samples include gilding and fresco paint. The results did not solve all the problems connected with these phenomena. The investigation revealed the presence of paraffin, closely linked to the treatment which Tintori completed in 1956. In these samples there is no presence of Paraloid 872, which was used in the last treatment in 1970. It is clear that it is very important to examine closely another group of samples.

e) Ion chromatography investigations to identify and quantify the anions of soluble saffs

A significant presence of sulphate is contained in this sample. These efflorescences are confined to a small area and are not responsible for the widespread whitening effect present on the pictorial film. However this datum confirms the neoformation gypsum, due to sulphation of calcium carbonate, found on the surface with EDS microprobe. Small quantities of chloride are also present . It is probable that these salts are connected with infiltration of water coming from the roof. (Tab 1)

Tab 1 - Dosage of soluble salts sample 12 15.5 1.3 0.4

5. CONCLUSIONS From initial analysis of the paint film as it was at the beginning of the present conservation work, and comparison of photographs taken before and after the action taken by the Central Restoration Institute (l.C.R.), it is reasonable to suppose that their action consisted of light cleaning and above all the application of a film of Paraloid 872 to consolidate the plaster base and paint film, and lend 1668 clarity, brightness and transparency to the dulled surface. After a further twenty-five years, the damage visible was probably due in part to the drying out of the paintings as a result of the change in the micro climate caused by the repairs to the roof and the guttering. The colours of the frescoes had dulled considerably and had acquired a shine, especially on the background blue; it was assumed that this shiny appearance was the result of the l.C.R. 's application of a film of Paraloid 872 over an earlier layer of wax, probably used in the previous more drastic restoration by Tintori. Three series of retouching were noted: some dating from earlier restorations, some done by Tintori in the 1950s and still others carried out by the Institute in the 1970s; one example of extensive retouching of a substantial area of missing original is in the St. Zachary. There are many repainted areas in the blue backgrounds. There were only a few examples of plaster that had become detached since the last restoration, confirming that the consolidation techniques used by the Institute were largely successful. The investigations carried out give some explanation of the state of conservation of the mural painting and of the materials used. The pictorial technique used , is fresco technique and the pigments are traditional. Repainting are present, in particular are evident on background, on cornices of false brick there are remaking. A dark thin protective film was found in some sample and probably is responsible of shining effect. Sometimes a dark patina is visible also on some gilded part, very probably due to the presence of tin lamina, more sensible than gold to humidity and water infiltration from the roof . Two different cases of size gilding are present (both with oil mordant mixed with coloured pigments, as adhesive): a) Gilding with tin lamina. This technique is known and were used in the past; in this case was employed where it was necessary to have more relief because is thicker. It is represented, for example, in the rays of the light that form the aureoles of the Saints. In the case of sample 15 in which are present two tin lamina, it is probable that there is a casual overlap of tin leaves. b) Gilding in which only gold lamina is present, giving a brighter effect; this kind have a limited distribution. The analysis carried out to determine soluble salts revealed the presence of a consistent amount of sulphate as gypsum, but this compound is not responsible of shining effect that has a large diffusion on the mural painting and is persisting after the cleaned Chemical and physical analyses were carried out and these confirmed that the whitening was not due to saline efflorescence, that are present in small area, but paraffin may be responsible of this phenomena. As regards infrared analyses, it is necessary to repeat some investigations on a greater number of samples because the presence of micro crystalline wax is a positive but partial result. From documents the last intervention were carried out using Paraloid 872 of which we don't find any traces.

ACKNOWLEDGEMENTS

The authors would like to tanks Mr. John David Millerchip, Co-ordinator of Private Committees for Safeguard of Venice, for the precious help in the English translation.

REFERENCES

R.J. Gettens, G.L. Stout, Paintings materials, New York 1966. M. Matteini, A. Moles, La chimica del restauro, Firenze 1989. R.L. Feller, N. Stolow, E.H. Jones, On picture varnishes and their solvents, Oberlin (Ohio) 1959. G.G. Amoroso, V. Fassina, Stone decay and conservation, Elsevier, Amsterdam 1983. AA W , La fabbrica dei colori, Roma 1986. C. Lock Eastlake, Methods and materials of painting the great schools and masters, Toronto, 1960. M.M. Merrifield, Original treatises on the arts of painting, New York 1967. J. Plesters, Cross section and chemical analysis of paint samples, Studies and Conservation, volume 2, number 3 , Aberdeen, April 1956, pp 110-157.