3.1 Assessment of the Biodeterioration Susceptibility of Stone Consolidants
The Metropolitan Museum of Art
The Getty Conservation Institute
Robert J. Koestler
Period of Activity: 6/86 to 12/87
The prevention of deterioration of stone materials used in works of art and in construction is of widespread interest. While many studies have considered the physical and chemical mechanisms that contribute to this deterioration, fewer have focused on the particular problem of biological attack on these materials. This study represented a large-scale attempt to screen preservative coatings for microbial susceptibility prior to their application on objects. It is clear that microorganisms exacerbate deterioration of stone and that any coating or consolidant placed on the stone should not provide a medium upon which microbes may grow.
After considering the combined effects of organism growth, sporulation, weight change, and chemical change, it was concluded that, in regard to fungal deterioration:
a.) Rhoplex AC234, Tegovakon V, and AYAA had high resistance.
b.) AYAC, Conservare H40, Acryloid F-10, Imron 192S, and Dammar all showed poor resistance.
c.) AYAC was completely degraded by fungal action after two weeks of incubation.
d.) The remaining polymers and resins showed levels of resistance between those of the first two groups.
Suggestions for Future Research
This short-term test was meant as an adjunct to durability testing of consolidants and coatings and should be performed in concert with such testing. A field study is the next logical step in these studies. Key objectives of a field study would be to test the microbiological susceptibility of a polymer or resin with and without the addition of a biocide in mixed environmental conditions, and to test for any resultant alteration in the physical properties of the underlying matrix/polymer combination using standard materials testing methodology. Another area of importance to development of better consolidants is the quantification of the effects of various environmental factors on the physical degradation of the matrix/polymer system (e.g., acid rain or extreme exposure conditions).
Koestler, R. J., E. D. Santoro, F. Preusser, and A. Rodarte, "A Note on the Reaction of Methyl Tri-methoxy Silane to Mixed Cultures of Microorganisms." Proceedings of the 1st Pan-American Biodeterioration Society Meeting, Washington, D.C., ed. C. O'Rear and G. C. Llewellyn, Plenum Press, New York, 17-19 July 1986, pp. 317-322.
ABSTRACT-Samples of methyltrimethoxysilane (M?OS) cured at four different relative humidities were exposed for five months to cultures of organisms. Although visual observations showed fungal growth, scanning electron microscopic observations did not reveal surface marring. Fourier transform infrared spectroscopy showed little change to the chemical structures of M?OS over the exposure period. It is concluded that the use of M?OS to consolidate a dolostone monument in the Metropolitan Museum of Art's collection will not result in encouraging the growth and spread of the deleterious effects of the microorganisms currently in the stone.
Koestler, R. J., and E. D. Santoro, "Assessment of the Susceptibility to Biodeterioration of Selected Polymers and Resins," Final Report to the Getty Conservation Institute, July 1988.
ABSTRACT-The prevention of deterioration of stone materials used in works of art and in construction is of widespread interest. While many studies have considered the physical and chemical mechanisms that contribute to this deterioration, few have focused on the particular problem of biological attack on these materials. The present study represents what may be the first large-scale attempt undertaken in the conservation field to screen preservative coatings for microbial susceptibility prior to their application on objects. It is clear that microorganisms exacerbate deterioration of stone and that any coating placed on that stone should not provide a medium upon which microbes may grow.
Sixteen polymers and resins important in preserving art materials, particularly stone, were evaluated for their ability to support fungal growth. Growth of the organisms was ascertained by macroscopic, microscopic, and physicochemical changes of these materials over a five-week testing period. Based upon their sensitivity to fungal deterioration, the polymers and resins tested were ranked in order of least to most susceptible to biological attack. The materials that were least affected were G.E. Silicone 1048 G.E. and Conservare H40; the most affected were Dammar and Acryloid B-72.