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3 rd^ SEMESTER: Conservation of Art and Archaeological Objects National Museum Institute, Delhi Topic: Bioreceptivity (Stone materials) The term bioreceptivity was introduced by Guillitte (1995) with reference to stone artifacts and subsequently expanded to cover all cultural heritage refers to- ‘the aptitude of a material to be colonized by one or several groups of organisms without necessarily undergoing any biodeterioration’ or as ‘the totality of material properties that contribute to the establishment, anchorage and development of fauna and/or flora’. The nature of the materials, i.e., their differing compositions, surface roughness, porosity, as well as their state of preservation, are all important factors in the establishment and development of organisms that could, in various ways, lead to the deterioration of artworks. The different stages of the colonization processes are distinguished as primary, secondary and tertiary bioreceptivity. Primary bioreceptivity indicates the initial potential of a material to being colonized. Over time, as a result of the action of organisms and/or other exogenous factors, this becomes secondary receptivity. Finally, any human activity that interferes with the material (E.g., Consolidations, treatments with biocides, etc.), and therefore alters its characteristics, induces tertiary bioreceptivity. It is not always possible to distinguish biological damage of a purely aesthetic nature from structural damage with irreversible consequences such as the degradation and decomposition of materials. In case of inorganic materials, this is true where the microflora does not make direct nutritional use of the substrate, with the exception of mineral salts, which are more or less depending on the nature of the constituent materials. In some instances, the presence of organisms on a substrate does not seem to cause any discernable alterations, either in its chemical composition or in its physical characteristics (Realini et al., 1985; Pietrini et al ., 1985),
but much depends on the interval of time elapsed from the inception of biological growth. The development of some of the organisms are exceedingly slow, and the damage may not be noticeable for many years, or even decades. Some authors have spoken of an effect of bioprotection exercised by some organisms, as for instance in the case of lichens on porous stone in outdoor environments. This hypothesis is based on the observation that in some instances where lichens have not been present, alterations such as exfoliations, efflorescence of salts, disintegration, pulverization, and honeycombing are more widespread. These organisms would then be exercising a protective function toward the substrate, reducing the intensity of water exchanges and the effects of atmospheric agents of degradation such as wind, rains, pollutants, and saline aerosol (Arino et al ., 1995; Wendler & Prasartet, 1999). However, this is a complex issue and the biodeteriogenic activity cannot be ignored. The capacity of microorganisms and organisms to adhere to the substrate is very important, i.e., the ability to transform the substrate is very much depending on the good adhesion. While the evolved and complex organisms (lichens, mosses, higher plants) adhere to, and penetrate, the substrate with specialized structures such as rhizines, rhizoids, or actual roots, microorganisms attach themselves to the substrate by forming a biofilm. This phenomenon, which is a precursor to possible physical and chemical damage, begins with nonspecific reversible reactions, which are primarily dependent on the physical and chemical properties of the cell and of the substrate. Once the microorganisms are in the vicinity of a surface, they are able to create stable interactions through the use of specific molecules and structures (lipopolysaccharides, membrane proteins, flagella). Moreover, organisms that adhere to a surface often secrete extracellular polymeric substances (EPS), the function of which is to ‘cement’ them to the surface. This viscous, sticky layer of microorganisms, organized into complex associations and immersed in a
that can be radically different from the surrounding environment in terms of pH and chemical- composition. Biofilms can also absorb particles and corrosive atmospheric pollutants, thereby increasing the rate of speed in the chemical corrosion processes (Warscheid & Braams, 2000). References: Guillette, O. (1995). Bioreceptivity: A new concept for building ecological studies. The science of the Total Environment, 167 : 215-220. Realini, M., Sorlini, C., & Bassi, M. (1985). The Certosa of Pavia: A case of biodeterioration. In: Felix G. (Ed.), Proceedings of 5th International Congress of Deterioration and Conservation of Stone. Presses Polytechniques Romandes, Lausanne,2: 627-629. Pietrini, A.M., Ricci S., Bartolini, M., & Giuliani, M.R. (1985). A reddish alteration caused by algae on stone works. Preliminary studies. In: Felix G. (Ed.) Proceedings of 5th International Congress of Deterioration and Conservation of Stone. Presses Polytechniques Romandes, Lausanne,2: 653-662. Arino, X., Gomez-Bolea, A., & Saiz-Jimenez, C. (1995). Lichen colonization of the Roman pavement at Baelo Claudia (Cadiz, Spain) : Biodeterioration vs. bioprotection. The science of the Total Environment, 67 :353-363. Wendler, E., & Prasartet, C. (1999). Lichen growth on old Khmer-style sandstone monuments in Thailand. Damage factor or Shelter? In: Preprints of the 12th Triennial meetings, Lyon, ICOM Committee for Conservation. James & James, London, 2:750- Morton, L.H.G., & Surman, S.B. (1994). Biofilms in Biodeterioration-A review. International Biodeterioration and Biodegradation , 34 (3/4): 203-221. Pinna, D., & Salvadori, O. (2008). Stone and related materials. In: Plant biology for Cultural Heritage , The Getty Conservation Institute, pp. 128-149. Warscheid, Th., & Braams, J. (2000). Biodeterioration of stone: a review. International Biodeterioration & Biodegradation , Vol.46, No.4:343-368.
