Study of sulphation of Candoglia marble by means of micro X-ray diffraction experiments

This research is aimed at assessing the particular
kind of damage caused by the interaction between atmospheric
pollution and the marble surface of a magnificent late gothic
church,Milan Cathedral, restored in the early 1970s. On the basis
of visual inspections and diagnostic investigations the facade
appears to be seriously damaged by surface erosion and thick
black crusts; biological crusts, micro-fractures and detachments
are widely present.
This paper reports on SR-μXRD data collected at the Synchrotron
Radiation Source (SRS), Daresbury Laboratory, and
at the European Synchrotron Radiation Source (ESRF) from
selected samples, covered with black crusts, originating from
the Milan Cathedral facade. Mineralogical maps of the deterioration
layers have been recorded by two spatial resolutions
(5–100 μm), from the bulk of the stone material to the outer
layer of the black surface. These maps help in elucidating the
mechanism of formation of the black crusts.