Chemical-mineralogical characterization of historical bricks from Ferrara: an integrated bulk and micro-analytical approach

In this paper we present bulk X-ray fluorescence-X-ray diffraction (XRF/XRD) and microanalytical scanning electron microscope-electron microprobe analysis (SEM-EMPA) data on historical bricks from Medieval or Renaissance buildings of Ferrara (NE Italy) to provide insights into the nature and provenance of the raw material as well as clues on the sintering techniques. Chemical data indicate that the starting materials were obtained by mixing high Cr-Ni clay and subordinate sand (both quarried from the Po river alluvial deposits) with the possible introduction of a Na-rich flux component. Thin-section observation, XRD and micro-analytical data indicate the presence of key accessory phases such as pyroxene, amphibole, epidote and rare olivine in the pre-fired mineral assemblage, confirming the utilization of the Po river sediments. Recognition of neo-formation firing phases (e.g. melilite, wollastonite), together with composition of micas, amphiboles and interstitial glasses, indicate kiln temperatures between c. 800 and 1000 degrees C. This provides guidelines for making new compatible and durable bricks to be utilized for restoration, and contributes to the preservation of historical masonry.