ELSEVIER

I~uernational Biodrrrriorarion & Biodegradation. Vol. 40, No. 2-4 (1997) 161-169 :(: 1997 Elsevier Science Limited

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Preliminary Study on the Biodeterioration of Canvas Paintings from the Seventeenth Century

by microchiroptera

R. F. Rubio” & F. C. Bolivarb*

“A.C.R.A. c/Maestro Faus No. 7, IA. 18008 Granada, Spain hDepartment qf‘ Pintura, Faculty Bellas Artes, Universit_s of Granada, 18071 Granada, Spain

This work focuses on the peculiar alterations found on various canvases from the refectory of the Carthusian monastery in Granada. The works studied were by the Baroque painter from Granada, Juan Sanchez-Cotin. During the study, the biological origin of these alterations was confirmed as being due to the products excreted by vespertilionid chiroptera, which roost in the summer on the corner braces of the stretchers of these paintings. These excretory substances have seriously deteriorated the images, causing blank areas and even total loss of the canvas, preparatory layer and pictorial strata. During restoration, it was confirmed that the excretory material of these bats continued to be active and hampered correct application of conservation treatments. Consequently, it proved necessary first to study and treat the excretions, which sharply lowered the pH of canvases. The zones impregnated with urine, extending from the upper to the lower braces, were neutralised, thereby stabilising the weak areas and providing satisfactory conditions for subsequent restoration treatments.

Este trabajo se centra en las peculiares alteraciones encontradas en varios lienzos del Refectorio de1 Monasterio de la Cartuja en Granada. obras de1 pintor barroco granadino Sanchez Cotan. Durante el estudio fue confirmado el origen biologico de estas alteraciones, debidas a 10s productos de excretion de microquiropteros vespertilionidos que reposan en epoca de estio en 10s angulos de refuerzo de 10s bastidores de estos cuadros. El inter-is de este trabajo radica en el hecho de que estas sustancias de excretion han dado lugar a importantes deterioros, destacando la formation de lagunas por perdida total del soporte textil, la capa de preparation y el estrato pictorico. Durante la intervention de restauracion. se pudo comprobar que las sustancias de excretion de estos mamiferos voladores continuaban activas e impedian la aplicacion correcta de 10s tratamientos de conservation y restauracion. De este modo, se hacia necesario el estudio y tratamiento previo de estas excreciones que provocaron una fuerte bajada del pH. Se procedio a la neutralization de las zonas impregnadas de orina, que se extendian desde 10s Lngulos superiores a 10s inferiores de la tela. consiguiendose la estabilizacion del debilitamiento existente y un resultado satisfactorio en 10s posteriores tratamientos de restauracion. R 1997 Elsevier Science Ltd. All rights reserved

INTRODUCTION was restored in 1963 (Orozco-Diaz, 1994). Together with the Alhambra, it is one of the

A relatively uncommon alteration in works with a canvas support was recently brought to our attention when undertaking the restoration of paintings in the Carthusian monastery in Granada, a sixtennth-century monument that

most visited monuments in Granada due to the artistic interest of its sacristy, cloister and painting collection.

The works treated are located in the refectory (Fig. 1) and were painted by Juan Sanchez-Cot&r, whose artistic output in Granada was prolific.

*Author to whom correspondence should be addressed. Originally from Toledo, he came to Granada as a

161

162 R. F. Rubio, F. C. Bolivar

Fig. 1. Location of canvases in the refectory of the Carthusian monastery in Granada.

master painter of beautiful works on wood. He is perhaps best known for his scenes of the martyrdoms of the Carthusians by Henry VIII in England, and for his still lives reflecting the austerity of monastery food at the time (Orozco- Diaz, 1993). Most of these works are found either in this monastery or at the Museum of Fine Arts in Granada. Two doctoral theses (Alonso, 1995 and Rodriguez-Barbero, 1996) have recently underlined the importance of this painter.

The paintings studied were completed around 1612 on Sanchez-Cot&-i’s return from the Carthusian monastery at Paular: After the dissolution of the monasteries, the paintings were used to decorate the altars in Bibarrambla Square during the celebration of Corpus Christi (Orozco-Diaz, 1993). Attempts were made to cover the numerous imperfections caused in the works by repainting (painting on top of the original).

On beginning the urgent task of restoration, it was seen that live of the paintings had one or several lacunae near the upper corners, some 10 cm from the edge (Fig. 2) comprising a loss of paint, while some also included a loss of the

preparatory layer with the appearance of efflorescences. In the worst case, the canvas itself was missing (Fig. 3).

The possibility that the origin of the imperfections might lie in water leaks was discarded after determining that there was no dampness on the walls or leaks in the ceiling. There was likewise no trace of city birds, which tend to be common in open cloisters. Vandalism was also dismissed, since the areas affected were in the highest parts of the paintings beyond the reach of visitors.

On examining the backs of the canvases, it could be seen that there were discolourations and rings due to some type of fluid running down them and originating next to the corner braces of the stretchers (Fig. 4). Although the stretchers are very old, they are not the original ones. They seem to have been made from leftover materials as some of the pieces are polychromed, probably having been part of a decorative area such as a retable or altarpiece. Paintings that have been rebacked and, therefore, have a new stretcher show no such alterations. The stretchers on the altered

Biodeterioration qf canvas paintings 163

Fig. 2. Alterations on the fronts of four canvases.

canvases were not fulfilling their function, as there were no wedges to help stretch the canvas. They had been made with wooden braces held by nails placed some 30cm from the corners to join and reinforce one brace to another (Fig. 5).

Numerous rodent-like faeces were also found on the stretchers and on the backs of the canvases (Fig. 6).

MATERIALS AND METHODS

The four paintings by Sanchez-Cotan (1560- 1627) from the refectory examined in this study were: ‘Monks Dragged towards Martyrdom’, ‘The English Judge Sentences Four Priors of the Order to Death’ (Fig. 7), ‘The Dream is Fulfilled, Saint Bruno and his Six Companions are Presented Before Saint Hugh’ and ‘The Funeral at which Saint Bruno Founded the Order’.

Several samples were taken for analysis by scanning electron microscopy (SEM; Zeiss DSM

950), for which they were fixed and dried to critical point at the Scientific Instrument Centre, University of Granada (Fig. 7). Samples that did not resist the fixing, washing and drying treatments were only coated with gold or carbon, which was the case with most of the samples from the layer of paint.

Chemical elements and alteration products were analysed by SEM-EDAX. The faeces were examined under the microscope.

RESULTS AND DISCUSSION

Analysis of the faeces revealed that they originated from a mammal whose diet consisted mainly of flying insects (principally Dipteru and Lepidoptera), in other words bats of the family Vespertilionidae. This family includes 38 genera and almost 300 species (Harrison Matthews, 1977). In this particular case the bats were Pipistrellus pipistrellus, which use the backs of the paintings as a resting place during the day.

164 R. F. Rubio, F. C. Bolivar

Fig. 3. Phot .ogra Iph showing loss of preparatory and paint layers, efflorescences and even loss of 1 the (

On the front of the paintings, whitish-grey damp stains that were heavily cracked could be seen. On the back we determined the presence of guanophile microorganisms (Fig. 8(l)), which produce acids (Samarra & Carol, 1986). The canvas comprised fibres from the stalks of Linum usitatissimum L. Microanalysis detected the presence of phosphates, calcium sulphate and calcium carbonate crystals, silicates and nitrates due to dissolution and recrystallisation (Fig. 8 (2-4)). These results concur with the analyses of urine and faeces of insectivorous bats by Studier & Wilson (1983) and Studier et

al. (1994a), . The added presence of lead and cadmium could

possibly explain why the microorganisms have only recently appeared on the canvas. Cadmium

:anvas.

has only recently been used in painting and, therefore, must be due to restorations in 1963. Other elements such as sulphur, iron, potassium, magnesium, aluminium, lead, calcium and barium indicate the use of traditional pigments, such as white lead, ochres, siennas and red lead oxide (Mayer, 1988).

Results of the analysis allow us to suggest a probable sequence of events in the biodeterioration of these paintings (Fig. 9):

(a) First we have a picture painted at the beginning of the sixteenth century with the normal layers of paint on canvas (Fig. 9(l)). (b) During the Inquisition the wooden stretch- ers were used for burnings at the stake. The canvases were, therefore, rolled up, adding to

Biodeterioration of canvas paintings 165

34 Fig. 4. Alterations on the backs of canvases, showing the structure of the stretchers with braces and the seams of different pieces of

canvas.

the normal cracking in the paint produced over time (Fig. 9(2)). (c) Colonisation by microchiroptera occurred after the restoration in 1963, at which time the stretchers with braces were put in place. The bats began to impregnate the canvas with urine and faeces, causing hydrolysis due to chemical and microbiological action (Fig. 9(3)). (d) The urine and acidic substances in the fermentation react with the carbonate and calcium sulphate, dissolving it and causing it to swell. Efflorescences are another result. Animal glues are also easily affected by urine, with a subsequent decrease in their adhesive capacity (Fig. 9(4)). (e) The urine then affects the paint and varnish layers. The varnish yellows due to oxidation and dissolution, with the urine acting as a strong, long-lasting stripping agent. The cracked paint layer is infiltrated by urine and

looses its underlying layer. It then forms curled chips that flake off, leaving behind remains of the preparatory mixture (grey in this case), as yet undissolved (Fig. 9(5,6)). (f) This process ends with the breaking of the cellulose chains in the canvas fabric which, although it is the first material affected, is the last to disappear (Fig. 9(7)). This loss causes a complete loss of all the layers in an area of up to 30cm* of canvas (Fig. 10).

In short, the preparatory layer is seen to be the most susceptible to the action of bat excrement and urine due to its very hygroscopic and solu- ble organic and inorganic components. In most cases this layer is swollen, showing up as crys- tals with no stability and no adherence to the canvas (efflorescences).The layer of paint with- stood the acid attack of urine better, since oil- based paints are more stable in the face of at- tack than carbonates or calcium sulphates held

R. F. Rubio, F. C. Bolivar

Fig. 5. Back of painting showing a non-original stretcher with corner braces and an area impregnated with excretions.

Fig. 6. Microchiroptera excretions affecting back of canvas.

together by the organic glues used in the pre- paratory layer. The greatest causes of alteration in the paint have been caused by the movement and loss of the preparatory layer.The canvas support is the most resistant material to this at- tack due to the structure and cellulose nature of the fibres (Agati et al., 1990) which are highly resistant to acids.

Response to restoration treatments

The process of biodeterioration caused additional problems for the restoration of these paintings. Since some areas were lifted and there was the risk of loosing paint, the traditional treatment for a work on canvas was adopted. An emergency protection treatment was applied, consisting of a layer of fine paper with Italian colletta (animal glue) in order to fix the paint chips and give this layer some cohesion.

Overall, this procedure gave satisfactory results except in the areas affected by bat urine. After several days it could be seen that the Italian colletta had dried and stiffened the canvas; nevertheless, the urine-affected zones were still damp and gelatinous indicating that the effect of excretions is long-lasting.

Fig. (‘Th

7. Locations of samples taken from one of the paintings e English Judge Sentences Four Priors of the Order to

Death’).

( 3ven the reaction of the animal glue in these are; as, we decided to re-examine the entire traditional

Pro cess of restoration of an affected painting, i.e., the application of a piece of cloth on the back of the pail nting using a paste of flour, Italian colletta and

Biodeterioration of canvas paintings 167

b)

:G” 8K 5.166 k&J 10.3 >

ch 268= 108 cts HEtll:iWJERSO PINTURA MRRFIL/l !

Fig. 8. (a) Microphotograph of microorganisms affecting canvas fibre. (b) An element microanalysis of the front of the painting. (c,d) Microphotograph of mineral phases in the efflorescences.

other ingredients. Since one of the components of this mixture is Italian colletta and this glue is definitely water soluble, there could be problems of adhesion in the canvases, the rebacking and any other subsequent treatments with this glue, such as reapplying lost preparatory mixture.

This conclusion led us to consider two possibilities:

(1) to discard treatments using water-based adhesives (the lack of effectiveness having been proven here), and substitute them by other systems with synthetic or wax-resin products (not apt for warm climates); or (2) to treat the affected areas and neutralise the effect of the excreted substances on the linen cloth and paint layers.

The second option was chosen, which also al- lowed us to neutralise the preparatory layer with animal glue, thereby employing traditional stucco work with calcium sulphate and colletta (Fig. 1 l).Due to the acidity of the urine compo- nents (Studier & Wilson, 1983) we opted for an

effective method to lower Iibre acidity (Fig. 11 (1)). For the neutralisation we used pads of dis- tilled water on the back of the canvas, soaking up excess water with a sponge (Fig. 1 l(2)). The fibre began to recover its natural colour and to lose the dark tone it had; the process was re- peated until the water absorbed by the sponge was not discoloured (Fig. 11(3)).The evident risk of this treatment was the abundant humidity that the canvas and other layers had to deal with. To counteract this problem (Fig. 9), heat and pres- sure were applied between each sponge treatment to remove any dampness rapidly and avoid dis- figuring the cloth. The rebacking was then car- ried out with full adhesion and no other problems were encountered (Fig. 11(4)).To pro- tect the paintings from other alterations, the stretcher (which was not the original) was ex- changed for a conventional reinforced one with- out braces.Measures are currently being examined to prohibit the access of chiroptera to the refectory, which is normally open 24-h a day to the monastery cloister. The alterations caused

168 R. F, Rubio. F. C. Bolivar

6

.>:.>>:.::: . . . . . . ..y.,. Ll $$& Varnish layer

q Paint layer

,,,,,l

q :::::: I,,,,, :::::: Preparatory layer

r-l Canvas

Area affected by excretions

Fig. 9. Probable sequence of events in the biodeterioration process: (1) original paint layer; (2) effects of cracking; (3) impregnation of canvas with urine and faeces; (4) impregnation and loss of preparatory layer; (5) advanced stages of impregnation affecting paint and varnish layers; (6) loss of paint and varnish layers; and (7) breaking of fibres in

canvas fabric.

by the bats are evidently subsequent to the re- storation in 1963 by the painter Manuel Lopez- Vazquez. We are also considering placing nets at the back of the paintings to protect them from resting while still allowing air circulation.We did not contemplate erradicating these bats from the area as they are protected by law. Indeed, they remove a great quantity of nocturnal diptera and lepidoptera, which dirty the backs of can- vases, as is the case with flies and moths (Tinei- dae).Many further studies and analyses remain

Fig. 10. End result of biodeterioration process.

to be done to understand and avoid this curious and little-researched alteration of valuable heri- tage paintings.

REFERENCES

Agati, A. P., Coldagelli, M. C., Consoni, C., Merucci, C., Minunno, G., Rorro, A., Seratini, 1. & Torrioli, N. (1990) I Supporti Nelle Arti Pittoriche. Storia, Tecnica, Restauro. Parte Seconda, Mursia Ed, Milano.

Alonso, M. L. (1995) Analisis estilistico y material de la pintura de Juan Sanchez Cotan. Tesis Doctoral, Universi- dad de Granada.

Harrison Matthews, L. (1977) La Vida de 10s Mamtyeros, Vol. 16, p. 131. Historial Natural Destino, Destino, Barcelona.

Mayer, R. (1988) Materiales y Tecnicas de1 Arte, p. 687. Hermann Blume, Madrid.

Orozco-Diaz, E. (1993) El pintor Skhez Cot& Servicio de Publicaciones de la Universidad de Granada.

Orozco-Diaz, E. (1994) La Curtuja de Granada Everest, Leon.

Biodeterioration of canvas paintings 169

Fig. 11. Process of canvas neutrahsation: (1) initial stage of alteration of canvas back; (2) sponging with distilled water; (3) advanced neutrahsation stage; and (4) final aspect after rebacking.

Rodriguez-Barbero, A. (1996) Analisis estetico plastic0 de las series pictoricas de Sanchez Cotan en la Cartuja de Granada. Tesis Doctoral, Universidad de Granada.

Samarra, F. X. & Carol, A. (1986) Les Ratespinyades. Bioiogia de1 grupo, aspectes bioespeleoldgicos, la seva distribucid i estudi a Cutalunya. Escola Catalana D’espeleologia, De- partament de Ciencies.

Studier, E. H. & Wilson, D. E. (1983) Natural urine

concentrations and composition in Neotropical bats. Comp. Biochem. Physiol. 75, 509-5 15.

Studier, E. H., Sevick, S. H., Keeler, J. 0. & Schenck, R. A. (1994) Nutrient levels in guano from maternity colonies of big brown bats. J. Mammol. 75, 71-83.

Studier, E. H., Sevick, S. H., Ridley, D. & Wilson, D. E. (1994) Mineral and nitrigen concentrations in feces of some Neotropical bats. J. Mammol. 7, 674680.