Successful combination of chemical and biological treatments for the cleaning of stone artworks

The removal of sulphate-based crusts from stone artworks using sulphate-reducing bacteria (SRB) has been proven to be an effective cleaning procedure. However, some concerns still remain: it is a time-consuming process when the crust is thick, and it is not clear how the biotechnological approach can fit within a complex conservation treatment. To address these challenges, the effects of an SRB strain (Desulfovibrio vulgaris subsp. vulgaris ATCC 29579) coupled with a non-ionic detergent pre-treatment was studied on a stone column affected by black crusts. The coupling of the two treatments removed the black crust without affecting the original sound marble, with 38% reduction in cleaning time. The combined method was later applied to a one-century-old artistic marble statue weathered by sulphate-based crusts and grey deposits. The detergent used alone effectively removed the grey deposit, but not the black crust. However the co-treatment synergy resulted in the complete removal of the black crust layers, with the added advantages, compared to the biocleaning alone, of fewer biological applications and a 70% reduction in total cleaning time, but still retaining all the advantages of the biocleaning approach.