Non-invasive technologies to timely screen out different application conditions of essential oils on stone

The use of EO (essential oils) either alone or in mixture has become a very attractive option as a green method to remove biological infestation from outdoor stone, but it still needs research for defining the most appropriate conditions of application. The aim of this paper is to screen the effectiveness of seven plant EO (alone or in combinations) taking into account key factors for obtaining a satisfactory treatment, such as: (i) the proper concentration/application timing ratio and (ii) the best poultice to enhance the performance of EO. Several combinations of these factors were applied on a marble slab naturally colonized mainly by phototrophs. The assessment of the organisms vitality, as an indicator of the treatment efficiency, was tested by using two portable and non-invasive techniques with an immediate response: the autofluorescence of the phototrophic pigments and bioluminescence of the adenosine triphosphate (ATP) molecule. Microphotography and colour measurements were also used. The most efficient treatment was then successfully applied on a real marble statue (Archaeological Museum of Florence, Italy).