Early detection of biofilm development on stone monuments thanks to pulsed IRT and SVD

IRT has been used as a first investigation in laboratory to detect pioneer biofilms which help the biological fouling of stone monuments. Biological development is often removed because of the unsightly aspect and it favours stone deterioration with mineral dissolution by production of organic acids, salting induces physical damage which helps to the development of macroscopic vegetation. Biological deterioration leads to the degradation of stone monuments and to the irretrievable loss of artefacts for our Cultural Heritage. Two limestones, Courville and Savonnieres stones used in major buildings in eastern France and the surroundings of Paris have been investigated. On first, stone samples have been exposed in outdoor test to favour the natural colonisation of first micro-organisms. They have been collected after six months exposure and compared to three non-colonised stones throughout IRT measurements of stone surfaces pulsed by a flux of photons. First results on Courville stone, showed Look Up Table (LUT) was important to emphasize slight variations of static images between stones with biofilm and control stones without it. Moreover, mathematical post-processing as SVD, usually applied to decrease thermal artefacts at the surface of a work of art and to improve detection of flaws inside it, here was to detect biofilms as surface artefacts thanks to the first EOFs. Savonnieres stone, which has different intrinsic properties than Courville stone showed static images can induced artefact associated to experimental conditions which was avoided thanks to SVD post-processing.