Thermoclastic and cryoclastic action on calcareous building stone: durability to artificial ageing

Short and long-term climate changes are a critical factor of stone decay even in temperate Mediterranean areas, when the combined fluctuations of temperature and moisture lead to thermoclastism and cryoclastism. The effects of weathering are of particular concern in the conservation field, for the assessment of the vulnerability of outdoorexposed stone materials in the historical built heritage. An example of this outline is Apulia, a region of southern Italy characterized by warm, dry summers and mild, rather rainy winters that can bring sub-zero temperatures; here, climate-driven decay can seriously affect the state of conservation of the local calcareous stone used in the monumental heritage, especially the most porous and softest materials. The dynamic behavior of the Apulian calcareous stone in response to thermo-hygrometric stresses was studied here by means of an artificial accelerated ageing test, focusing on a single local stone variety known as “pietra gentile”. It is a fine-grained, soft and porous calcarenite, which is exploited in the Murge area from the outcrops of the “Calcare di Caranna” Fm. (late Campanian?–Maastrichtian). The quarrying activity is concentrated in the territory of Valle d’Itria and mainly of Ostuni, touristically known as “the White Town”, where the stone is widely used for the sacred and civil architecture. The ageing test was programmed according to the typical climatic characteristics of the considered area, following the historical recordings by the official Apulian monitoring institute (Struttura di Monitoraggio Meteoclimatico, Centro Funzionale Regionale); in order to simulate the seasonal climatic changes, the extreme temperatures were considered, while the possible insolation effects for higher temperatures were also taken into account. So, samples of “pietra gentile” were subjected to 100 temperature cycles from 60 to –5 ◦C, in a climatic chamber with a maximum relative humidity of 60%. Before the ageing, the samples were petrographically characterized through optical microscopy on thin section, followed by a geotechnical parameterization with petrophysical measurements (dry density, total porosity, MIP porosity) and indirect ultrasonic and sclerometric tests. Then, after every 20 ageing cycles, the same tests stated above were carried out; in addition, the measurement of residual strains and SEM observations were performed. With this methodology, the gradual modifications in fabric, petrophysical and mechanical properties of the tested stone were analyzed.The results revealed a high durability of the material to the conditions of ageing experimented. The main modifications of the samples concerned fabric, i.e. microcracking due to thermoclastic and cryoclastic action, which occurred only in limited areas for an uneven distribution of internal stresses. For this reason, no evident effects on the macroscopic integrity and physico-mechanical performance were noted, whereas the stone almost preserved the original strength and elasticity. Finally, the data gathered were used to suggest a method for the evaluation of the vulnerability of “pietra gentile” to freeze-thaw microcracking, based on the peculiar porosimetric distribution and the environmental conditions of weathering. New information are globally provided about a stone material that has been largely used in the Apulian monumental heritage, but has received scarce attention from the archaeometric research so far

Exploring the raw materials and technological practice to obtain red and black surfaces of Apulian red figure pottery by Raman and SEM‐EDS investigations

In this paper, 4th century BC Apulian red vases, from sites among the most relevant in Apulia (Italy), are studied by means of Raman spectroscopy. The effectiveness of this technique in the archaeometric research is emphasized, particularly regarding the manufacturing procedures and raw materials of black and red surfaces. Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDS) analyses are carried out jointly with Raman spectroscopy in order to complete the morphological and chemical information. The results show that two different clays have been employed for black gloss and ceramic body. The black gloss proves composed of the finest fraction of terre rosse—very common all over Apulia—with no organic material added to its clayey suspension. Traces of carbon found on the surfaces can be ascribed to fly ash deposited during the firing process. This research highlights that two more methods besides red engobe were used by Apulian potters to color red the surface of whitish/grayish vases realized with local raw materials, namely, the addition of either “miltos” or a clayey layer enriched in Fe oxides. A multistep firing (ox-red-ox), reaching the maximum temperature of about 900C, can be deduced from the different mineralogical phases identified through Raman. The possibility of gaining information on the hematite particles size from the position of its characteristic Raman bands is successfully investigated, allowing to get clues on the presence of a surface layer in a nondestructive manner by comparing the particle size there and in the ceramic body

Glazed sgraffito ware from Torre Alemanna (Foggia, fifteenth to sixteenth century A.D.): technological aspects of a local production

The archaeometric investigation of 46 potsherds of “Torre Alemanna type” pottery aimed to define a compositional refer- ence group and to understand the technological characteristics of its production. Principal component analysis applied to bulk chemical data (XRF) of the ceramic body showed a strong compositional homogeneity. Their comparison with local clays and 6 fragments of bricks sampled from the ceramic kiln, on the one hand, revealed the use of alluvial clays as raw material and, on the other hand, proved their fractionation for the production of pottery. The mineralogical assemblages detected by X-ray powder diffraction analysis inferred maximum firing temperatures between 750 and 1000 °C for the ceramic body. Polarising optical microscopy and scanning electron microscopy with energy dispersive spectroscopy (SEM–EDS) investigations on coating revealed the presence of quartz-rich white engobe covered with a high lead transparent glaze. The polychromatic decoration was analysed by colorimetry and EDS to compare the colour characteristics through all the pot- sherds. A temperature range between 780 and 950 °C of liquidus temperatures was inferred from the ternary phase diagram of PbO-Al2O3-SiO2 system. Overlap of temperature ranges for sintering of the ceramic body and maturing glaze points to a single firing of the Torre Alemanna type ware. The results obtained define the reference compositional group and technol- ogy of the Torre Alemanna type ware, already attested in several archaeological contexts of southern Italy, and showed a technological continuity with the past about the use of local carbonate-rich clays to produce fine pottery

Understanding the origin of magnetic znomalies in Monte San Vincenzo (Southern Italy) archaeological Site: susceptibility measurements, PXRD, XRF and optical analysis

In the 2002 a multidisciplinary research project began studying the ancient landscapes of Tavoliere, an agricultural area located in Southern Italy that, as shown by historical and archaeological documentations, has been intensively populated from the Neolithic until the Middle Ages (e.g. Bradford, 1949; Jones, 1987; Volpe, 2001). Since the number and extent of the sites (villages, villas, farms, necropolis, etc.) render the planning of a systematic programme of excavations very difficult, a ..