Laboratory Model to Investigate the Effect of Cold Plasma in Cleaning Fungal Contamination from the Surface of Stone Cultural Heritage

Microorganisms are considered as one of the most important factors in the deterioration of tangible cultural heritage, which can cause irreversible damage to historical monuments and artefacts, and lead to the loss of their artistic, aesthetic values. Therefore, cleaning and removing living organism by different methods is one of the conservation treatments, which are carried out in the field of restoration and preservation of historic and cultural objects. It is very important to choose the cleaning method and the strategy to deal with microorganisms according to the nature and condition of the historical monument. The efficiency of new methods of restoration and cleaning have been less the subject of restoration and conservation research in the country. The purpose of this study is to adopt a suitable method to evaluate the efficiency of cleaning of stone heritage contaminated with Aspergillus niger fungus using atmospheric cold plasma in a laboratory model.According to theoretical principles and ethical considerations concerning the conservation and restoration of cultural heritage, a laboratory model was designed for this research. Hence, carbonate stone similar to historical sample was obtained from Pasargadae region. Stone specimens were contaminated with Aspergillus niger strain MJ, which was stored in the microbiology bank of Alzahra University, used for inoculation on stone samples. After inoculation, stone samples were incubated for ۶ months. Some stone specimens were considered as controls and three non-thermal plasma regimes, including dielectric barrier discharge, gliding arc and jet were used to clean Aspergillus niger from stone.In order to investigate the effectiveness of the plasma-cleaning methods and whether they meet the needs of conservation and restoration area, an approach integrating complementary techniques were used, including colorimetry, optical microscopy, scanning electron microscopy and x-ray diffraction. Color changes, morphological and compositional features of the surface of samples were studied before and after inoculation by Aspergillus niger, and also after cleaning. The results showed that the fungus has grown well on the carbonate stone and in some cases the presence of halite and oxalate caused by the metabolite of the fungus was observed. The obtained results showed the reduction of the microbial load of this type of fungus by using three plasma regimens, although the structure of stone was changed. Accordingly, laboratory modeling of cleaning methods is necessary before any conservation treatment to less the damages before any implementation. More research should be performed on the introduction of proper laboratory methods to evaluate the cleaning techniques for different substrates.

کلیدواژه ها:

Carbonate stone ، Deterioration ، Fungi ، Biomineralization ، Decontamination ، Cold plasma