An approach to the study of the fungal deterioration of a classical art material: Mastic varnish

Mastic, one of the best natural varnishes, is frequently used as protective and finishing layer or as component of oleo-resinous media in paintings, both in the past and currently. However, this resin is affected by complex deterioration processes which can change its characteristics and thus the visual aspect of works of art. The alteration processes caused by radiation have been widely studied, but there is a lack of information on the biodeterioration of this natural product. In this paper, fungi from collections as well as from oil paintings of the Fine Arts Museum of Granada (Spain) were inoculated onto slides covered with mastic. The samples, after an incubation period of 15 days, were analysed by gas chromatography-mass spectrometry (GC-MS) to identify the chemical changes undergone, and a visual monitoring of the samples was performed to determine the formation of mycelia onto solidified resins. Major changes were detected in Chrysonilia sitophila, Phoma herbarum, and P. chrysogenum, showing evidence of alteration processes caused or favoured by these microorgamisms.

Biodeterioration patterns found in dammar resin used as art material

Since the middle of the XIX century, when dammar became popular in Occident, this natural resin is one of the most used in art painting techniques as final protective coating (varnish) as well as a component of pictorial media. The present work is the first approach to the study of the microbiological biodeterioration of this artistic material, which can seriously affect the appearance and integrity of works of art when bad conservation conditions -especially high humidity levels- take place. 12 microorganisms, fungi and bacteria, came from collection and from oil paintings affected by biodeterioration patterns, were inoculated on test specimens prepared with varnish dammar. These were incubated and analyzed by GC-MS to determine both the microbiological capacity of growth and chemical alteration on the resin. Some of the studied microorganisms have shown patterns of deterioration similar to those found in works dedicated to natural or accelerated photochemical ageing of triterpenoid varnishes.