###### Abstract  
During the last restoration campaign of the Baptistery of San Giovanni in Florence (Italy), the assessment of the state of conservation of external surfaces was performed, with a multi-analytical approach, in order to support the conservation and restoration treatments. Black crusts, red staining, sulphation, and organic patinas were identified. Moreover, a complete characterization of marble cladding, bricks, and mortars was carried out. A geochemical and minero-petrographic approach was used in order to classify and assess the provenance of marbles, and define raw materials and technologies of the production for bricks and mortars. Provenances from Italy (Carrara and Lasa marbles) and from Greece (Hymettus and Pentelicum marbles) were identified and attributed to different construction phases, restoration interventions, and re-use of ancient materials. For mortars, the obtained data suggested the use of local materials and traditional technologies for the production. Overall, two different minero-petrographic typologies were identified for the analyzed bricks.  
San Giovanni Baptistery; Florence; decay and alteration phenomena; marbles; mortars; bricks 202220220220220220220220220220220220220220220222022202202220222022202220222202222022220  
stratifications of the Baptisery, the OPA promoted a great opportunity for integrated multidisciplinary research and studies to achieve a fuller historical and scientific knowledge about the stone materials used in the Florence Baptistery.  
This paper focuses on the characterization of cladding marbles, masonry materials (mortars and bricks), and on the study of their state of conservation. Different kinds of materials (white and veined marbles, mortars, bricks) were analyzed, often belonging to different constructive phases, with the purpose being not only to obtain a complete knowledge of the material, but also to identify the provenance, raw materials, and technologies of production.  
The provenance of white marbles, especially Mediterranean ones, is of great interest for archaeologists and art historians, but it is also one of the most debated problems of petroarchaeometry [6]. In recent years, it has been demonstrated that the application of minero-petrographic and geochemical methods, along with the comparison of data  
Figure 1: San Giovanni Baptistery in Florence (photo taken from the terrace of the Santa Maria del Fiore Cathedral).  
with dataset obtained from quarry samples, allows us to suggest the provenance of white marbles [6; 7; 8].  
In the case of marble slabs of the Baptistery, the research is aimed at identifying reused ancient marbles, the original ones used, and the more recent substitutions.  
For the cladding materials, specific research on the main phenomena of alteration/decay and on the presence of traces of previous restoration interventions was carried out in order to address the restoration procedures.  
In previous studies, other stone materials were identified, coming from the spolia of Roman ruins in Florence or Fiesole (Porfido Verde Antico, Porfido Rosso Antico, Breccia Greca Antica, Syenite) [9]. Local stones, such as serpentinites (verde Prato) and red marly limestones (\"marmi\" rossi), were identified and characterized in other Florentine monuments [10; 11; 12; 13].  
The paper presents a description of all sampled materials and of the chemical, mineralogical, and petrographic techniques, including optical microscopy (OM), X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), micro-Raman, and \({}^{13}\)C and \({}^{18}\)O isotopic analyzes used to gain a better understanding and characterization of the present materials, as well as their provenance and state of conservation. The results consist of, first of all, an evaluation of the main decay phenomena that affect especially white marble surfaces, an assessment of provenance of white and veined marbles, and a characterization of mortars and bricks.