Műtárgyvédelem 23., 1994 (Magyar Nemzeti Múzeum)
Tanulmányok - Nemessányi Klára: Kalcium-oxalátok előfordulása és kialakulása falképeken és köveken
THE OCCURRENCE AND FORMATION OF CALCIUM OXALATES ON MURALS AND STONES Abstracts: During the course of restoration work, the author found an indelible light brown layer of patina on a mural of Italian origin dated to around 1510, painted using the al fresco technique. This layer was composed of calcium oxalate. It may either have developed as the result of the microbal decomposition and transformation of a protective casein layer or as a consequence of a heavy fungal contamination: one of the fungus species identified produces oxalic acid. In Siklós (Southern Hungary), oxalic acid was found on the murals of a Gothic sanctuary. This should be considered peculiar, since one is dealing with a spacious ente- rieur, in which no visible patina is apparent. Still, X-ray diffraction tests were indicative of oxalates in 14 of the 16 samples gathered. According to the author’s hypothesis, structural changes of the material observed in these cases were caused by bacteria or fungi. In the international literature calcium oxalates were, almost without exception, mentioned as occurring on stone and wall surfaces as well as natural rocks found in the open air. The presence of patina was attributed exclusively to lichen activity by Monte and Sabbioni (1987). Two years later, Lazzarini and Salvadori described that oxalate patina may also occur as the result of oxalic acid excretion by certain species of fungi and bacteria or the application of a protective casein coating respectively. To date oxalate patina has been identified on medieval wall remains and stone material at four different locations in Hungary. The peculiarity of these find spots is that most of them are located in internal spaces. This, by definition, excludes lichen activity but makes the earlier influence of other microorganisms such as fungi and bacteria more likely. Szerző cime/Author’s address: Nemessányi Klára festő-restaurátor/painting conservator 1021 Budapest, Labanc út 39/b. 54
