The artificial stones in the liberty architecture of Florence: from characterization to restoration

In the second half of the XIXth century the diffusion of the new hydraulic binders made it possible to produce artefacts of particular hardness and durability in imitation of natural stone. The use of these artefacts, known as artificial stones, spread throughout Europe with a maximum use at the beginning of the XXth century. These materials fulfilled the demand for ornamental architectural elements making it possible to achieve a remarkable speed in the realization of decorations and simplifying their installation with a significant economic benefit. In Florence, between the XIXth and XXth centuries, the presence of decorative elements made of artificial stone in imitation of Pietra Serena, Pietra Bigia and Pietraforte is quite diffused in the Liberty style buildings. The artificial stones consisted of a mixture of binder (usually Roman Cement, Portland Cement or White Cement) and aggregate (sand, pebbles, ground stone), often admixed with pigments; the mixtures were generally lean. Artificial stone artefacts were produced in particular "ateliers" by artisan-craftsmen under the guidance of masters who developed recipes of different mixtures according to the requirements of the buyer. The artisan products were made in moulds or directly "on site" thanks to the use of mouldings (galvanized sheet profiles) in order to produce objects of different shapes and sizes. Once made and after sufficient seasoning, the artificial stones were later worked and finished with the tools of masonry and sculptors. The recipes for the realization of fake stone are often unknown because they are kept in craft shops and handed down only orally. Scientific research on these materials is therefore of great importance especially for the purpose of conservation and restoration of the liberty monuments. In this work we have characterized the artificial stones used in some Liberty Florentine buildings: Casa Carnielo Gallery, Vichi Gallery House, Villino Uzielli, and monumental cemeteries (Trespiano, Rifredi). Petrographic, mineralogical and chemical investigations were carried out in order to highlight some of the fundamental characteristics of these materials such as binding/aggregate ratio, binder nature, choice and selection of the aggregate, presence of soluble salts etc. These data, together with those on the technology of realization (mould or directly on site) have been taken into account both to identify the production techniques of the various "ateliers" and to understand the decay phenomena. As a matter of fact, the known durability of this material, mostly made with Roman Cement, which provided greater preservation with respect to the artefacts made with Portland, are compromised in the decorative elements where metal frameworks have been utilized which in many cases need adequate restoration work and appropriate maintenance programs.