This contribution is intended to present a biennial research project, funded by the MIUR-PRIN 2009, dealing with innovative experimental approaches applied to the analytical study and the restoration of ceramic finds recovered from underwater archaeological excavations. The project involves three Research Units belonging to the University of Catania, the University of Cosenza and the University of Palermo. The central assignment of this project comes from the concern that during the last decades only a limited interest was dedicated to the study of degradation processes affecting archaeological ceramic in seawater environment (LEMOINE et alii 1981; BÉARAT et alii 1992; PRADELL et alii 1996). This was likely due to the complicatedness in simulating the processes leading to the compositional and/or physical modification of ceramic artifacts during their marine burial. Alteration and/or degradation of ceramic involve numerous variables which are related to the intrinsic characteristics of the ceramic paste (i.e. packing, size, distribution and composition of the temper grains, composition and texture of clayey groundmass, size distribution of pore spaces, etc.,) as well as to the conditions provided by the aquatic medium (i.e. temperature, pH, Eh, biological activity, salinity, etc.,). It has to be underlined that the current analytical approaches taking significantly into consideration the chemical modifications of the ceramic objects can be mainly addressed to the so called “provenance studies”. In fact, the alteration and contamination processes involving archaeological ceramic in burial environment (BUXEDA I GARRIGÓS J. 1999) can seriously interfere with the assignment of the object to a specific production center, issue of decisive importance in the reconstruction of ancient economic history. In the above descrive framework is positioned the present research project, which is mainly focused on the investigation of chemical, mineralogical, physical and mechanical transformations occurring during the permanence of ceramic in seawater. The experimental part of the research, currently in progress, is accomplished on a series of ceramic test-pieces (briquettes and cylinders) purposely manufactured in order to reproduce consistent compositional and textural characteristics. Ceramic briquettes were placed in specifically designed and man-made Ertacetal® (acetal copolymer) stamped cover shields, and kept in two open underwater environments correspondingly characterized by monitored oxidizing or reducing conditions (Fig. 1). In contrast, ceramic cylinders were placed in custommade glass containers partially filled with two different types of bottom sediment, under a continuous seawater flow of around 5 liters per minute (Fig. 2). The main physical-chemical parameters being monitored and controlled as well. Both the above described experimental equipments are hosted at the protected harbor of the Italian CNR-IAMC (National Research Council - Institute for Marine and Coastal Environment) next to Mazara del Vallo, Sicily. A fructuous partnership with researchers and technicians belonging to the above mentioned institution was truly realized. Cylinders and briquettes will be periodically collected within four different steps (3 months, 6 months, 12 months, 18 months) in order to investigate the different forms of alteration and deterioration developed and to quantify the modifications occurred into the designed ceramic pastes under different conditions. The research project can be schematically shared into different steps. An initial effort has been already dedicated to the upgrading of the scientific literature on the subject. This was considered important for preparing a proper starting point for the experimental part. During the same step a large number of archaeological ceramic samples were collected from the late Roman relict at Cala Tramontana in the island of Pantelleria, under the supervision of the Sicilian Soprintendenza del Mare in order to be fully characterized. During the subsequent phase the already cited ceramic test-pieces (briquettes and cylinders) were produced using well studied Sicilian raw materials (clays and sands with individual mixing and tempering procedures). In particular, two different types of materials, a calcareous clay and a non-calcareous one were mixed with two categories of sand temper, respectively of volcanic and sedimentary nature. The obtained experimental pastes were accordingly fired at different temperatures under oxidizing kiln atmosphere. In the meantime, all the customized experimental facilities have been calculated and realized (Ertacetal® cover shields, glass containers and the whole plumbing system). The next strictly analytical steps of the research are going to be focused over the revision of the different forms of inorganic alteration/deterioration that likely will develop in the exposed briquettes and cylinders. Biological aspects will be also considered and accurately investigated paying special attention to the subject of biomineralization. The correlation between physical and chemical transformations and compositional or textural features will be carefully examined. The discrepancy of the bulk chemical composition of the ceramic test-pieces before and after the experimental exposure to seawater will be measured. In the cylinder shaped test-pieces the before/after changes in composition will be also appraised between the parts exposed to flowing seawater and the parts placed at various depth in the sediment. Moreover, a quantitative model for calculating the correction factors concerning the most relevant major and/or trace elements will be considered. This latter outcome could be used for comparable authentic case studies (i.e. coastal areas in the Mediterranean Basin), thus arising a satisfactorily level of transferability of knowledge. Another important issue to be developed within the present research consists in the identification and increase of optimal conservation procedures. In fact, different techniques for the extraction of marine salt from the ceramic body will be comparatively tested and proposed as innovative and more efficient procedures. They are expected to be purposely suitable for laboratory fieldwork during submarine archaeological research and for the preliminary treatments preceding the museum exhibition of the most precious findings. In addition, innovative methods for encrustations removal as well as consolidation and protection treatments for this category of archaeological ceramic finds will be tested.
|Titolo:||Innovative experimental approaches applied to the study of ceramics from underwater archaeological excavations|
|Data di pubblicazione:||2012|
|Appare nelle tipologie:||1.1 Articolo in rivista|