NON-DESTRUCTIVE METHODS USED IN THE MONITORING OF RESTORATION INTERVENTIONS ON THE MEDIEVAL FRESCOES.

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1 NON-DESTRUCTIVE METHODS USED IN THE MONITORING OF RESTORATION INTERVENTIONS ON THE MEDIEVAL FRESCOES Ion Sandu 1, Constantin Luca 2, Irina Crina Anca Sandu 3, Viorica Vasilache 1, Ioan Gabriel Sandu 2 1 Al.I.Cuza University of Iasi, Romania 2 Gh. Asachi Technical University of Iasi, Romania 3 Universidade Nova de Lisboa, REQUIMTE-CFQB, Lisboa, Portugal lilly75flower@yahoo.com Abstract The paper deals with the one-year monitoring of the evolution of the conservation stat e and effects of restoration treatments of indoor frescoes of Probota Monastery s church (XVIth century, Moldavia-Romania). The frescoes and the indoor microlimatic agents were studied "in situ" with the help of a series of non-destructive analytical methods and the obtained data were correlated for pointing out the behavior of the interventions during the four seasons two with humid climate and two with dry one. The cleaning of frescoes done in major part by students (that did not controlled very well the concentration in cations/anions and ammonium carbonate) arose problems regarding the appearance of efflorescences in the change of the microclimatic conditions from a season to another. There were also evaluated the consolidations with Primal and barium hidroxyde. 1. Introduction and type of methodology The Church of the Probota Monastery (1530), is one of the seven churches with ind oor and outdoor frescoes from northern Moldavia, which are included in the UNESCO list of the World Cultural Heritage (1993), at the position 397. In 1996 began the restoration and conservation of the entire site trough an UNESCO Project, financed by the Japan trust Fund, ending in Beginning with 2001, the Monastery was reintroduced in the tourist circuit and of course was monitored during the entire period in order to establish the reliability of the preservation-restoration interventions on the frescoes(1-3). Due to its age and its precarious conservation state, six types of operations were involved in the consolidation and stabilization processes: pre-consolidation of the painted layer; consolidation of the fragile painted layer; re-adhesion of the painted layer to its mural support in order to prevent flaking; cleaning and the leveling of the painted layers in order to minimize the diffusion (scattering) effects, responsible for the blurring of the colors; consolidation of the intonaco at the interface intonaco/arriccio; consolidation of the arriccio at the interface arriccio/plaster (4-9). The present paper is a study concerning the modifications of the physicalstructural and chemical characteristics of the indoor frescoes after its restoration. Physical-chemical, chemical properties and biological investigations P79

2 2. Type of parameter that is preferentially measured The saline formations (10) resulted from the effect of efflorescence at the surface of the indoor mural paintings, bo th on the northern and southern walls and also on few dividing walls inside the church, were initially photographed under reflected light and than taken trough detachment by brushing with a fine brush and finally analyzed through IR spectroscopy in order to evaluate their nature. The nature and evolution of the saline efflorescence ( 10) were determined after the sampling through chemical qualitative analyses and through direct observation with a magnifying glass under reflected light. For the quantitative analysi s of the salts the method of extraction with paper pulp in ion-mg/100g compress was used. The IR Spectra were done with a Perkin-Elmer SP-200 spectrophotometer, using the method of the dispersion in KBr, underlining the specific band of absorption for certain organic and inorganic compounds, in the domain cm -1 (1). The analyses through IR spectroscopy were done on samples taken from Naos, Burial Chamber and Pronaos, from the southern and northern walls. The normal domain of variation of the hydrous equilibrium for intonaco and arriccio was studied based on the variation curves of the dehydration processes of the samples that were humidified into water and of the hydration of the samples that were thermally desiccated in static regime at 65ºC, for cca. 6 hours (until a constant weight of the samples) using a thermo regulated oven (1-3). 3. In situ application There were studied the areas affected by the saline efflorescence, inside the chambers with important thermal and hydrous fluctuations. As the analysis of the normal domain of variation of the hydrous equilibrium is concerned, samples from the same structural elements: intonaco and arriccio from the old preparation layers that were presented in (1-3). The monitoring of the interior micro-climatic conditions and of the thermal and hydrous parameters of the mural paintings were done with a system of electronic thermometers and hygrometers placed into the walls at the surface of the frescoes at different levels, beginning with 0,1 m from the floor till 2,5 m high (3). The humidity of the wall, at the level of the interior layer of preparation ( arriccio ), was determined by GANN Hydromette compact B, on the principle of high frequency measurement, while the temperature of the wall was determined with the help of electronic thermometers placed in the wall at the level of the interior layer of preparation ( arriccio ). 4. Evaluation of methodology/technology used The figure 1 shows the photographs with the areas from the southern walls of the Naos and Burial Chamber, affected by the efflorescence (a) and the microphotographs under reflected light of the saline formations at the surface of the frescoes, 1,8 m high from the floor (b). P80 Physical-chemical, chemical properties and biological investigations

3 a b Figure 1. Image of the surface saline efflorescence from Naos (first line) and Burial Chamber (second line): a the iconographic register of the affected area by the saline efflorescence; b microphotography of the saline formations from the frescoes. The Table 1 is giving the data concerning the quantitative analysis, expressed in ion-g/100 g compress, that are verified between the limits for the table n. 2. Table 1. The values of the salts quantity extracted from walls, using the paper pulp method Sample no. The place where the sample was taken from The content of ion-g /100 g compress - NO 3 2- SO 4 Na + + NH 4 1. Naos, southern wall Naos, northern wall Burial Chamber, southern wall Burial Chamber, northern wall Pronaos, southern wall Pronaos, northern wall The Table 2 is giving the chemical nature of the saline formations resulted from the efflorescence effect. The data is confirming the presence of the saline formations (hexahydrate natrium nitrate, beautifully crystallized, microcrystalline and mat calcium sulphate, residual crystals of ammonium nitrate and ammonium chloride traces) on both the southern and northern walls and even on dividing walls inside the church. Physical-chemical, chemical properties and biological investigations P81

4 Table 2. The results of chemical analyses of the saline efflorescence Legend: - lack; + present in small quantities; ++ present in large quant.; +++ present in very large quant. The Table 3 is giving the domain of wave numbers characteristic to the active structural groups of the efflorescence s salts from the IR spectra. Table 3. Wave numbers of the absorption bands of the main components from the crystallized salts in efflorescence Sample Efflorescence in Naos Efflorescence in Burial Chamber Wave numbers (cm -1 ) , , , 1400, , , , ( ), , , , Attributions Hygroscopic water, network water, hydration water and chemically bound water from hydroxide groups Organic polymeric compounds, resulted from consolidation Carbonates Nitrates Silicates Hygroscopic water, network water, hydration water and chemically bound water from hydroxide groups, more strongly activated Organic polymeric compounds, resulted from consolidation Carbonates Nitrates It was an expected fact that after the cleaning interventions with ammonium carbonate the major part of the soluble salts from the preparation layers were activated. The surprise consisted in more abundant saline efflorescence on the P82 Physical-chemical, chemical properties and biological investigations

5 southern walls compared to the ones on the northern walls. Moreover, the interior walls, that are dividing the chambers of the church, presented also a saline activity. The analyses showed that the efflorescence activity is based on the hexahydrate natrium nitrate and on the dihydrate calcium sulphate and in a minor quantity on ions of phosphate and chloride. The first one forms crystalline, opaline efflorescence, the lasts are giving microcrystalline, mat efflorescence. The presence of the ammonium ion demonstrates the negative effect of the cleaning with systems based on ammonium carbonate, without controlling its concentration. Moreover, the presence of the ions of nitrate, sulphate, carbonate and silicate in the IR spectra is explained by the low level of humidity in the church (RH under 60%). The Table 4 is giving the values of the humidity and temperature of the walls in the interior area of the preparation layers (under arriccio ), determined at three levels of height from the floor: 0,50 m, 1,00 m and 1,50 m, at middle of June There is a good correlation between these data, in accordance with the diagrams of the hydrous equilibrium in function of temperature, specific for the composite materials. Table 4. Values of renderings humidity (% weight) and of temperature (ºC) in several points from the Naos, Burial Chamber and Pronaos (month of June) The Table 5 i s giving the limits of t he dehydration processes of the humidified samples and of hydration of the dried sa mples, that configure the normal domain of variation of the hydrous equilibrium for intonaco and arriccio. Table 5. Values of th e limits that configure the normal domain of variation of the hydrous equilibrium fo r intonaco and arriccio. Sample U u * (%) Ue(d)* (%) U r * (%) U e (h)* (%) Untreated Intonaco ~25 <1,0 <0,25 >2,0 Treated Intonaco ~20 >1,0 >0,25 <2,0 Untreated Arriccio ~20 <0,5 <0,15 >1,5 Treated Arriccio ~15 >0,5 >0,15 <1,5 *) U u exceeding humidifying humidity; U e (d) equilibrium humidity resulted for dehydration at R.H. 60% and t = 20±3ºC; U r residual humidity obtained afte r drying in oven at 60ºC, for 4 hours (till a constant weight); U e (h) equilibrium humidity obtained after the hydration processes at R.H. of 99% and t = 20±3ºC for the dried samples. From the data featured in Table 5 results the fact that the effects of the consolidation interventions influence both the humidifying capacity, which drops approx. 5% for both structural components, arriccio and intonaco, and also the equilibrium humidity level, which drops cca. 1%, to the normal domain of Physical-chemical, chemical properties and biological investigations P83

6 variation, that is between 0,5 and 2,5 %. These shifts do not lead to irreversible physical-chemical effects, which could negatively affect the interventions fiability. On the base of the results concerning the variation domains of the interior microclimatic parameters of the church, of the thermal and hydrous characteristics of the preparation layers and of the normal domain of variation of the hydrous equilibrium, the following levels of maximum and minimum can be established: the relative humidity of the air: under 30% and after 85%; the environmental temperature: under - 5 C and after 40 C. These minimum and maximum values can induce critical situation of precollapse for the structures of the conserved and restored frescoes. REFERENCES 1. I. Sandu, A. Dima, I.G. Sandu, C. Luca, I.C.A. Sandu, 2003, Monitoring the behaviour of the restoration interventions of the Probota Monastery s indoor fr escoes under the influence of the environmental factors. I., EEMJ 2, 1, I. Sandu, A. Dima, I.G. Sandu, C. Luca, I.C.A. Sandu, 2003, Monitoring the behaviour of the restoration interventions of the Probota Monastery s indoor frescoes under the influence of the environmental factors. II.Modifications of the Physical-structural and chemical characteristics, EEMJ 2, 4, I. Sandu, A. Dima, I.G. Sandu, C. Luca, I.C.A. Sandu, 2003, Monitoring the behaviour of the restoration interventions of the Probota Monastery s indoor frescoes under the influence of the environmental factors. III. Correlations between thermal, hygroscopic and sonic parameters, EEMJ 2, 3, P. Mora, L. Mora, P. Philippot, 1986, Conservation of Wall Paintings, Butterworths, London and Romanian version, Ed. Meridiane, Bucureşti. 5. P. Mora, G. Torraca, 1965, Fissativi per dipinti murali, Bollettino dell Instituto Centrale del Restauro, Rome, P. Mora, L. Mora-Sbordoni, 1993, The Nefertari conservation program, Art and Eternity: The Nefertari Wall Painting Conservation Project, , Getty Conservation Institute, Los Angeles, 67-81; 7. S. Peroni, C. Tersigni, G. Torraca, S. Cere a, M. Forti, F. Guidobaldi, P. Rossi-Doria, A. De Rege, D. Picchi, F.J. Pietrafitta, G. Benedetti, 1981, Lime based mortars for the repair of ancient masonry and possible substitutes, Proceedings of the ICCROM Symposium on Mortars, Cements and Grouts used in the Conservation of Historic Building s, ICCROM, Rome, V. Schostak, W. Funders, B. Recker, G. D rescher, H. Juling, 1995, Konservierungstechniken für die Wandm alerei in der Kirche in Eilsum/Ostfriesland, Maltechnik-Restauro, R. G iorgi, L. Dei, P. Baglioni 2000, A new method for conso lidating wall paintings based on dispersions of lime in alcohol, Studies in Conservation, 45, 3, I. Sandu, I.C.A. Sandu, A. van Sannen, 1998, Expertiza ştiinţifică a operelor de artă, vol. 1, Iaşi, Trinitas, 680. P84 Physical-chemical, chemical properties and biological investigations