The shielding effect of the protective glazing of historical stained glass windows from an atmospheric chemistry perspective: Case study Sainte Chapelle, Paris

Atmospheric pollutants, gases as well as particulate, have been pointed out as a major cause of weathering of historic stained glass windows. Although conservators did not succeed in stopping or reversing the ensuing damage up to date, a slower rate of destruction to maintain the grandeur of the artifact is certainly achievable, by installing a protective glazing (PG). Measurements were carried out for a period of 1 year in the Sainte Chapelle in Paris, France, in order to integrate the influence of some major pollutants and acidifying substances indoors, and outdoors, as well as in the interspace, created by the PG. The concentrations of SO2, NO2 and O3 were assessed using passive diffusion tubes. The PG reduced SO2 and O3 pollutant exposure of the stained glass windows by 80% relative to the outdoor concentrations. NO2 concentrations remained almost the same inside, outside and in the interspace; however, previous studies showed that even in high concentrations of NO2 accompanied by low concentrations of SO2 the degradation of this kind of glass is modest. The results of bulk particle analyses by energy-dispersive X-ray fluorescence indicated the accumulation and re-suspension of particles as the main factor of elevated concentration of elements inside of Sainte Chapelle. The abundance and type of particles obtained by electron probe X-ray micro analysis were slightly different in the three measured areas. The main distinction is the occurrence of CaSO4 particles inside and in the interspace. In conclusion, the installation of a PG in Sainte Chapelle seems to be appropriate.