CHEMICAL CHARACTERIZATION OF THE BLACK CRUST PRESENT ON THE STONE CENTRAL PORTAL OF ST DENIS ABBEY

A black crust sample from the stony central portal of the abbey of St. Denis, France, was analyzed by chromatographic and spectroscopic tech niques to determine whether it was due to atmospheric pollution or to the degradation of a past restoration treatment. Stratigraphic surveys by optical microscopy, Fourier-transform infrared spectroscopy (FTIR) , scanning electron microscopy/energy dispersive X-ray fluorescence (S EM/EDX) and pyrolysis/gas chromatography/mass spectrometry (PY/GC/MS) were consistent in ascribing the bulk of the crust to gypsum (CaSO4 . 2H(2)O) with inclusion of carbon particulate. The organic fraction was a minor constituent of the black crust. Hence, the deterioration by a n organic substance used in the past to restore the building was ruled out.