The colour of the façades in Siena's historical centre. Calcium oxalate films on brickwork of XV-XVI century palaces.

Previous studies of entire brick façades of XIII and XIV century palaces in Siena revealed traces of ancient treatments of the surfaces for aesthetic purposes. It was also possible to attribute such treatments, today presenting as calcium oxalate films, to the time when the façades were built. The aim of the present study of several XV and XVI century brick façades is to determine if the same finishing techniques continued to be used in time. The results indicate that the palaces of this second period present similar types and distribution of Ca-oxalate films on the various architectonic elements of the façade, and confirm the aesthetic purpose of the original treatments. From the historical-architectural point of view, these conclusions reveal the diffusion of facing brickwork in high- and medium-prestige buildings during XIII-XVI century, and the so far unknown use of chromatic enhancement, via transparent and/or variable red shading treatments, to differentiate the wall face from the architectonic and ornamental elements.