Chemical-mineralogical characterisation of historical bricks from Ferrara: an integrated “bulk” and “in-situ” analytical approach.

In this paper we present bulk XRF/XRD and micro analytical SEM/EMPA data on historical bricks from Medieval/Renaissance buildings of Ferrara (NE Italy) to provide insights on 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 and 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 ~ 800 and 1000 °C. This provides guidelines to make new compatible and durable bricks to be utilised for restoration and contribute to the preservation of historical masonries. Ancient bricks from Medieval and Renaissance buildings of Ferrara (NE Italy) have been studied using bulk techniques that analyse a few grams of homogenised (powdered) sample, and micro analytical techniques that allow composition analysis of single phases of materials heterogeneous at micrometre scale. This characterisation provides useful clues to constrain the provenance of the original raw materials and the historical firing techniques. These data provide information useful to understand the physico-chemical behaviour of the studied bricks that will be helpful in future preservation and restoration strategies.