Microbiological deterioration of Gambara's frescoes exposed to open air in Brescia, Italy

Microbiological studies were carried out on samples taken from L. Gambara's deteriorated frescos, painted on outside walls of two buildings in Brescia, Italy, in the 16th century. The results showed that aerobic heterotrophic bacteria, fungi, ammonifiers and sulphur-oxidizing bacteria were present in all samples and in most cases were well above the levels considered damaging; only fungi and sulphur-oxidizing bacteria counts underwent variations relating to climatic conditions. Moreover, some fungi are able to grow in the presence of malachite and haematite, used as pigments for frescos, but not limonite. The same fungi change the green colour of malachite into blue.