Colour changes of Notos calcareous sandstone as related to its colonisation by microorganisms

Studies were carried out in order to correlate changes in colour of rock surfaces, with bioreceptivity of calcarenite stone used to built the Baroque town of Noto (Syracuse, Sicily) and the microflora associated with surface colouring defined as ‘orange and/or grey patinas’. Our results showed a different contribution of microorganisms to the orange and grey colouring of rock surfaces. Algae and bacteria are mainly related to the orange colour, while black pigmented microorganisms are strongly related to the greying of rock surfaces. Water availability and sun exposure control this different distribution of microorganisms. Noto calcareous sandstones possess a high bioreceptivity.