The change of building stone materials in Florence from Middle Age to Renaissance until XXth century

The building materials used in Florentine architecture from the archaic period (Roman period and then from the XIth century) until the XIXth century, are closely linked to the available stone materials cropping out in the hills surrounding the city, to its geographical position and to its history, characterized by a succession of architectural styles that produced substantial changes to the historical centre over the years. These materials, above all the Pietra Serena and Pietraforte sandstones, have been widely studied from the geological, mineralogical and petrographic point of view and also concerning their durability and problems of conservation. From the end of XIX century, in Florence, the artificial stone materials started to be used, particularly for architectonic decorations, thanks to the discovery of the modern hydraulic binders (Portland cement) which made it possible a production of decorative elements with the help of moulds. Therefore an artificial stone is produced mixing an hydraulic binder mixed with aggregate, pigments and water and pouring it into a mould; this mortar can reach the hardness and appearance of a natural stone (e.g. sandstone). The scientific studies on building stones materials used in Florence allowed to identify distinct varieties both within the two main sandstones (Pietra Serena and Pietraforte) and within the artificial stones contributing to a better knowledge of the building heritage of Florence.