The steeple spire of the Parma Cathedral: An analysis of the glazed bricks and mortars

In October 2009, a terrible lightning struck the steeple spire of the Parma Cathedral, causing a fire. The fire-fighting operation made possible the discovery of the original spire ceiling made up by dichromatic glazed bricks, white and black, dating from the 14th century. Original materials presented a relevant decay, both for the high temperatures reached during the fire and for lack of maintenance. The research presents the first study of glazed bricks of the 14th century in Po Valley (Italy) with the purpose of collect chemical, mineralogical and petrographic data on the dichromatic glazed bricks. Brick samples with different kind of glazes and mortars exposed at different condition of fire were analyzed. The following techniques were used in the study: X-ray powder diffraction, optical microscopy, scanning electron microscopy analysis, inductively coupled plasma atomic emission spectroscopy and Raman spectroscopy. Glazes, applied on to Ca-rich paste, have a high lead content (41–57 wt%), with an high amount of tin (19–24 wt%) for the white opacified glazes and manganese (about 4.0 wt%) for the black ones. Typological and historical analysis allowed us to define the production technique of bricks and glazes. Mortars are mainly composed of lime binder and carbonate aggregate.