The brick material culture of Urbino (UNESCO World Heritage, Central Italy) as inferred from a multidisciplinary archaeometric study on the historic architecture

Abstract

Roman to Modern times (19th century) brick samples from monuments, walls and other masonry buildings of the historic centre of Urbino were investigated through a multidisciplinary approach, including mineralogy and texture (thin section and XRPD), chemistry (major-trace elements), physical–mechanical properties and thermoluminescence (TL) dating, coupled with the historic literature data. TL mostly confirms the building periods of the architectural structures where the bricks were sampled, also emphasising for the Cathedral a building period that lasted more than three centuries. The supply areas of the raw materials seem to have always been the same through time, very close to the city to the West and Northwest, represented by the deposits deriving from the weathering of the Marnoso-Arenacea Formation, which was able to give both clays and sands (temper) for the bricks. Some historic documents of the second half of the 15th century reporting an act of sale of a person living in the western areas surrounding Urbino with a commitment to providing several thousand of bricks to the Cathedral factory, seem to confirm the geological constraints. The firing temperature should have been reached at least 850–900°C, as indicated by the presence of new phases such as gehlenite and clinopyroxene in almost all the investigated samples. Nevertheless, the failure to achieve complete thermodynamic conditions for both wide inhomogeneities in grainsize and composition of the raw materials and the lack of temperature control during firing, mostly gave rise to incomplete calcite breakdown. The absence of standardisation of the pyrotechnological processes probably led to the large variability of the physical–mechanical features even for bricks of the same building period. Uniaxial Compressive Strength of the investigated historic bricks, however, falls within the range of present-day full-bricks, and a general improvement of the brick quality from Roman to Modern times was highlighted, as well as a progressive refinement in preparation techniques before firing. The brick material culture of Urbino continues seamlessly, after the investigated periods, until the second half of the 20th century, testified by the presence of the brick factory of the Fornace Volponi, just outside the historic centre of the city.