The secret of the artisans of Salento: diagnostic investigations applied to the study of the finishing techniques of the baroque buildings of Lecce (Puglia, Italy)

The city of Lecce (Puglia, Italy) known internationally thank s to the local stone handicraft and to the precious historical and artistic monuments, owes its title of "Cradle of the Baroque" to two types of rock: pietra leccese and carparo. These two rocks belong to the group of miocenic limestone and of quaternary limestone, respectively. The formation of soil of Puglia dates to the quaternary and tertiary periods and soil is characterized by limestone with chemical and physical characteristics very different from each other and with satisfactory colors. Thanks to their quality pietra leccese and carparo were the materials mostly used by local artisans for the construction of buildings located in Salento peninsula (Puglia-Southern Italy) since ancient times. The complex baroque architecture of the city of Lecce was also produced: significant examples are the pinnacles, the decorations, the capitals, the statues that decorate the facades of the baroque buildings of the city of Lecce. In these buildings, public or private, laic or religious, the bricks of the facades sometimes were left untreated, more often were finished with inorganics or organics for aesthetic, hygienic or protective purposes. Knowledge of the finish materials applied on the facades of these buildings is important to plan a correct restoration and to preserve the cultural heritage and the tourism of the city. However, there are several difficulties such as the scarcity of written sources, since the finishing techniques used in the past were jealously preserved by artisans, and, mainly for organics, the phenomena of alteration and degradation that inhibit the identification of the techniques employed. A multidisciplinary research, which involved the study of the few written and oral sources, has allowed the identification of some organic products, which possibly were applied by the artisans of Salento on the surface of the buildings constructed between the 1600 and 1900 centuries: among these products, there are also natural materials whose usage was not hyphotesized before on cultural stone heritage. In the present work laboratory specimens of pietra leccese and carparo, treated according to the already known and knewly discovered recipes and subjected to natural and artificial aging, have been studied, through the use of optical, colorimetric, spectroscopic and chromatographic techniques; the employed analytical methods were of great help to the identification of molecular markers, characteristic of the various organic substances, and to the characterization of methods, used in the past on the facades of baroque buildings of Lecce, revealing some secrets of the ancient artisans of Salento.