Per una rilettura della bicromia sulle superfici murarie medievali in Umbria

Combination of differently colored materials in building cladding links the decorative 'design' of the surface to the basic architectural structure. The realization of these works - already studied in architectural and artistic fields - is based not only on the availability of appropriate materials, but also on the accurate organization of the construction site, in which different experts are present during the planning and the building phases. Due to a systematic classification of the Umbrian Middle Ages masonries, it's hereby suggested reinterpreting the building techniques thema, at the same time considering the decay of the surfaces studied. The presence of bi-chromatic elements in architecture is noticed in Europe since the end of VIII century but it appears in Umbria only during the X century, where reaches its maximal technical accuracy between the 1300s and 1400s. In Perugia, Assisi, Foligno, Spoleto, Gubbio, Spello, Todi and Sangemini were built entire walls made of white and pink limestone ashlars set up in alternate order to make lines, bundles or more complex structural decorations. Meanwhile, it can be observed that pink limestone can discolor, turning to white or to ocher (dark yellow), because of water, in a non-reversible way, sometimes confusing the formal interpretation of the original pattern of the masonries facing. It is possible to suppose that Medieval builders were familiar with the process of color degradation in some rocks. However they were not able to control the mentioned phenomenon; consequently they made structures that can now appear irregularly dressed only because of changes in color of stones.