RICERCA ITALIANA     

Research program

ATELIER, WORKSHOP, YARD. TECHNIQUES AND CULTURE OF THE PRODUCTION IN THE ROMAN WORLD

University Co-ordinator

Università degli Studi del SALENTO - BENI DELLE ARTI E DELLA STORIA - ()

Research Unit Leader

Giuseppe Egidio De Benedetto

Description

The Salento (Lecce) R.U. will carry out chemical investigations on the materials coming from excavations of the Vesuvian area, and eventually from other areas, if necessary to solve peculiar archaeological issues. In this respect Bologna and Parma research units will allow both interesting exchanges of data and experience, and the possibility to analyze a significant number of samples aiming at a definition of the techniques and the materials employed in the building (mortars and binders) and the decoration (painting, mosaic, stucco, in the decorated layer and in the support) of the Roman age in Italy and in the Vesuvian area in particular. Investigations on Cisalpina painting materials will be carried out alongside those on materials excavated in the Vesuvian area, selected by the Bologna R.U.-Archaeology dept, to verify the occurrence of similar materials and techniques.
The analysis of the wall mortar will take place in critical points selected from the DISTART R.U., in order to determine the composition of wall binders in various stages of construction, with particular reference to superelevations and antique restorations, to find out the solutions with whom the ancient cantiere addressed the needs and emergencies that they had during the life of buildings.
These archaeometric investigations will supply important information for the knowledge and valorization of the sites of the Mediterranean area and will contribute to a better definition of the net of interconnections and of cultural and commercial exchanges in the Basin itself.
The gained knowledge will provide a wealth of useful data for the restoration of decoration and structures, which will be made available to the Soprintendenza Archeologica for conservative interventions.
The work program of the Research Unit (in collaboration with the Parma R.U.) will be the application of the modern instrumental analytical techniques to samples of wall paintings in order to discover the nature of pigment and plaster, and to binder samples (mortars) used in wall textures, especially in correspondence with the restoration interventions after the earthquake of 62 or consolidation in relation to height of buildings: in Pompeii and Herculaneum, in fact, occur numerous construction works designed to increase the height of Roman domus traditionally ground floor.
In addition any degradation effects generated by environmental conditions will be highlighted, and the actions of modern restoration often performed with camouflage criteria recognized and classified.
The data obtained by chemical and physical analysis could allow one to determine the gamut of pigments available at a local, regional or imperial scale, and to make some hypothesis about the color preparation and application techniques (thanks also to the possibility to determine any organic substances present, vide infra). Such information could enable the study the origin of pigments, the product trading and communication connections, up to define the characteristics of certain painting “atelier”. Pigment choice, in fact, depended both upon the availability of products on the market and upon the technical-scientific know-how of the painter. The characterization of pigments will be performed by in situ colorimetric analysis, infrared and Raman molecular spectroscopies, mass spectroscopy with plasma source (ICPMS). Some of these techniques make it possible to obtain information on the mineralogical species present in materials, others make possible to identify the composition of the chemical elements present as a major, minor or trace component.
Thin and polished cross section will be produced from samples of parietal painting. These samples will be studied first by optical microscopy. Since the samples under investigation are heterogeneous at microscopic scale, an analytical technique for solid samples should be used with sufficient spatial resolution to allow trace element analysis of the interesting regions (the single layers) while avoiding the inclusions. On the other hand selective knowledge of the elemental composition of these inclusions could be fundamental to solve the archaeological issues. LA/ICP-MS fulfills the aforementioned requirements thanks to its wide linear dynamic range, its low detection limits, its low sample consumption (micro-destructive technique) and its spatial resolution capabilities within a range from approximately a few micrometers up to 1 mm. Similarly both parietal and floor mosaic tiles will be studied.
The characterization of the chemical composition of the mortar will allow the study of changes in building technology and the identification of parameters that can discriminate chronologically different mortars. The scientific approach starts from the characterization of the material to reach the formulation of strategies for preventing degradation, for conservation and restoration. Comparative analysis will be made of mortars from different archaeological sites and the complete chemical analyses will possibly permit the identification of the chronological and technological differences.
Mortars will be investigated with the objectives of: a) characterize the binders used in the various phases of construction, b) compare the materials used in the same phase, c) contribute to the study of building technologies of different historical periods, d) compare the materials used in different geographic areas. Samples of mortar initially will be observed with a stereoscopic microscope to document the structure, the color (even with the help of a spectrocolorimeter) and consistency.
The granulometric analysis of samples by mechanical sieving (sieve meshes of 4, 2, 1, 0.5, 0.250 and 0.063 mm of diameter) will be carried out in order to obtain information about the grain size distribution and an estimation of the proportions of binder/aggregate within the mortar. The most significant granulometric fraction, that whose particle size is lower than 0.063 mm and containing the binder will be analyzed by FTIR and elemental analysis after disgregation by ICPMS. On the other hand, the chemical treatment with 2 M hydrochloric acid in order to determine the insoluble residue as well as the soluble salts extraction and determination by HPIC will be carried out. If necessary, XRD and thermal analysis (TGA–DTG) by Parma R.U. will complete the analytical work.s
The study of local techniques (in Cispadane) to achieve the heating, dehumidification, drying (barns and other deposits in rustic buildings), led by Bologna R.U., will benefit once again of FTIR spectroscopy to verify the structure exposure at high temperatures, and then determine whether suspensurae, pillars of brick or stone, were used to the flow of hot air produced from an unidentified heater, or only served to isolate the floor from soil humidity. In particular, the mineralogical nature will be examined aiming at finding neo-formation phases following heat treatment. The advantage of this innovative approach is high in terms of preparation and processing of samples (no dissolution necessary), cleaning and simplicity of the experimental procedure, time of analysis. If necessary XRPD analysis will be carried out in cooperation with the Parma R.U..

Organic materials in mural paintings and stuccoes
There is a growing interest in developing a methodology for the identification of organic materials used in paintings. The knowledge of the different types of organic materials in wall paintings and their behavior is fundamental for the development of appropriate conservation and maintenance procedures. Though important improvements have been made in this field, there is still much to be understood about the nature and role that organic materials have had in these handworks. In the last years, it has been developing analytical techniques for the identification of organic materials in ancient works of art. These methodologies make use of gas chromatography/mass spectrometry (GC/MS) and Pyrolysis GC/MS and allow to identify different organic materials from samples in the sub-millimetric range.
At first an analytical protocol will be defined and tested on samples of wall paintings of known composition. This phase corresponds to a feasibility study and has the objective to provide a model for the format and presentation of the analytical results and an assessment of the resources required to extend the study to complete the project. The project will continue with the application of the analytical protocol to a group of organic materials in wall paintings and stuccos of the Vesuvian area (Pompeii and Herculaneum).
EXPECTED DELIVERABLES
Mural decorations, mosaics, stuccoes, mortars, plasters:
A) chemical, morphological and mineralogical information on raw materials of tesserae, stuccoes, mortars and plasters; on the chemical nature of opacifiers, coloring and decoloring agents, pigments; B) archaeometric information: definition of composition patterns, morphological structure and mineralogical phases as a crucial step to infer reasonable hypotheses about classification and production technology as well to recognize eventual restoration activity not evidentiated by autoptic observation.
Organic substances:
A) identification of organic substances used in the production of mural decorations, in stuccoes, in plaster; identification of substances used in conservative operation; B) archaeometric information: identification of substances used in order to make possible hypotheses on technological production and use.