RICERCA ITALIANA     

SCIENCE OF ANCIENT MATERIALS DERIVED FROM GEO-MATERIALS:
basic Geosciences knowledge applied to the study of metals and glassy-materials

Università degli Studi di Pavia

Abstract

The project aims to: promote the advancement of scientific base knowledge and the transfer of technological know-how, produce scientific publications, and develop an on-line reference database. As research will be undertaken within university structures, the project will make the most of human resources by providing young researchers the opportunity to be involved in the research activities. The project aims to reach two main objectives which form the basis of project management and monitoring. The objectives are identified at the end of a series of tasks that lead to a well-defined result.

The project is a balanced mix of research activity, organisation and formation. Research will take place in laboratories which in time have acquired expertise and instrumentation for the micro- and nanometric characterisation of fragments smaller than a millimeter, but representative of the whole artefact and providing the accurate determination of their structure and chemistry.

OBJECTIVES
1- Identify methodologies and calibrate analytical strategies for the investigation of ancient materials.
2- Reconstruct ancient production recipes and processes through analysis.

TASKS
1) RAW MATERIALS IN THE PRODUCTION OF GLASS, EUTECTIC REACTIONS AND FUSION PROCESSES
2) STANDARDISATION OF ANALYTICAL METHODOLOGIES AND DATABASE DEVELOPMENT
3) GLAZE-CERAMIC BODY INTERACTIONS, RELATIONSHIPS BETWEEN SUBSOLIDUS AND LIQUIDUS SYSTEMS
4) METAL ALLOYS, SUBSOLIDUS REACTIONS, TEXTURES AND MICROTEXTURES ALSO DETERMINED BY PROCESSING
5) COMPOSITIONAL ZONING AND MIXING OF SILICATE MELTS FOR GLASS PRODUCTION

The project aims to produce original, at times innovative, scientific data from the study of archaeological materials ascribed to historical periods both when the production technology of metal and glass is attested and when important technological progress witnessed: the transition from the Bronze Age to the Iron Age in the production of metals, the change from the Roman (Na-Ca-glass) to medieval (K-Ca-glass) recipe for glass, the transfer of ceramic glaze production know-how from the East to the West. Although the project cannot resolve these complex historical issues, it aims to provide a coherent analytical base and substantially contribute to the reconstruction of technologies used to produce the investigated historical artefacts. <<<

Principal Investigator

Bruno MESSIGA Università degli Studi di PAVIA

Research Objectives

The project aims to: promote the advancement of scientific base knowledge and the transfer of technological know-how, produce scientific publications, and develop an on-line reference database. As research will be undertaken within university structures, the project will make the most of human resources by providing young researchers the opportunity to be involved in the research activities.

Basic research involved in this project is highly likely to find practical applications in artisanal (ceramics and artistic glass) and industrial (blown glass and flat glass) production. In the context of cultural heritage, this project will also provide a better understanding of cultural goods and enables the refinement of diagnostic protocols for their conservation and restoration.

The project is undertaken by a research group which aims to subsequently establish collaborations with European Community partners. At the end of the project the group will be able to continue its activities through various financial instruments identified among the specific measures in support of international cooperation. Objective B.2 - "Protection and conservation of cultural heritage" is encompassed in projects such as the present one, which adopts an integrated, multidisciplinary approach for the identification and valorisation of civilisation pathways in the Mediterranean area.

The research group was not established as a mere formality, but was defined on the basis of mutual acquaintance among participants, past collaborations and the complementarity of the different analytical laboratories. The group therefore reflects the natural aggregation of researchers who, in addressing issues from the standpoint of their respective disciplines, have understood that efforts must be coordinated to obtain innovative results.

OBJECTIVES

1- Identify methodologies and calibrate analytical strategies for the investigation of ancient materials.

In the initial pioneering stage ancient materials were studied by various geoscience research groups using their own analytical strategies and instrumentation. However, researchers have now identified the need to standardise analytical strategies for the production of data that can be easily compared and disseminated throughout the scientific community using on-line data bases. There is also a need to obtain homogeneous data from the different laboratories and establish procedures for the definition of analytical and process standards. The integration of the different methodologies adopted by the various groups will lead to the identification of suitable methodological approaches for solving specific problems linked to different artefact typologies and for addressing specific archaeological and archaeometric issues.

2- Reconstruct ancient production recipes and processes through analysis

This research topic is mentioned in FP.6 grants. Some research in Italian universities has shown that the study of ancient materials provides interesting ideas for research on ways to improve current industrial production, since it reconstructs methods for the production of durable material to use in the valorisation, conservation and restoration of buildings and cultural goods. It is therefore important to reconstruct the history of technological progress, and of cultural goods, especially the improvement of products through the empirical experience and culturally determined choices of specialised craftsmen. Research will undoubtedly contribute to archaeological studies, as specific analytical data on the intrinsic structure of materials may provide valid objective criteria for their attribution and discrimination.

TASK (Actions):

1) RAW MATERIALS IN THE PRODUCTION OF GLASS, EUTECTIC REACTIONS AND MELTING PROCESSES
Contribute to the systematic study of glass from different Italian and Mediterranean archaeological sites, which cover a wide interval of time spanning from the Bronze Age to the Middle Ages, with the aim of investigating the evolution of production technologies.

2) STANDARDISATION OF ANALYTICAL METHODOLOGIES AND DATABASE DEVELOPMENT
Given the intrinsic complexity and inhomogeneity of materials, it is extremely important to define analytical protocols for the establishment of reference analytical methodologies, and compositional and process standards for the creation of reference databases.


3) GLAZE-CERAMIC BODY INTERACTIONS, RELATIONSHIPS BETWEEN SUBSOLIDUS AND LIQUIDUS SYSTEMS
Model and experimentally verify the interaction between glaze and ceramic body starting from the measured chemical composition of a specimen of the vitreous coating-ceramic body interface. Notwithstanding the scrupulous studies so far undertaken to describe and model the interaction between ceramic body and glaze, there are still no comparative studies on contemporaneous productions but only studies on productions from different areas of the Mediterranean basin.

4) METAL ALLOYS, SUBSOLIDUS REACTIONS, TEXTURES AND MICROTEXTURES ALSO DETERMINED BY PROCESSING
Field archaeology and archaeometric laboratory investigations which focus on metallurgical production through the morphological, structural, textural and compositional characterisation of metallurgical slag and complex alloys such as bronze and iron materials.

5) COMPOSITIONAL ZONING AND MIXING OF SILICATE MELTS FOR GLASS PRODUCTION
The production of glass, i.e. of a mixed silicate melt, is a complex non-linear process that presents strong analogies with that of magma mixing. It is therefore possible to apply analytical and interpretative (modelling) methodologies used in the study of igneous rocks to the study of synthetic materials such as glass.

TASK vs Research Units (RU)

(1) MODENA - PADOVA - SIENA
(2) MODENA - PADOVA - PAVIA - PERUGIA - SIENA
(3) PAVIA - SIENA
(4) MODENA - PADOVA - PERUGIA
(5) PAVIA - PERUGIA <<<

First Results

The expected and final results are the achievement of the proposed
objectives and the publication of data in specialized journals <<<

Timescale

24 months

National and international background

The study of ancient materials focuses on the numerous factors that led to the production of artefacts with extremely complex intrinsic characteristics. For this reason archaeometric studies on production processes and transformation of raw materials must involve the integration of different analytical techniques. The reconstruction of ancient production and processing technologies, i.e. processing of raw materials, through scientific investigation is such that archaeometry can be considered a true Ancient Materials Science when it focuses on the relationship between the properties of ancient artefacts and their crystalline structure and texture.
In recent years one of the areas of principal collaboration between archaeology and earth sciences has been the study of geological materials used in the production of artefacts, analysed as indicators of provenance of handicraft items that show a degree of specialization that would seem to suggest a level of economic and social organization already involving craftsmen freed from the tasks of primary production and dedicated primarily or exclusively to their specialized skills. This fundamental transition in social complexity is first seen in Italy and Europe during the Bronze age, around 2000 B.C. It subsequently developed, merging into the historical period and achieving complete affirmation and articulation in the Roman age.

TASK 1 - The glass production implies different phases starting from quarrying of raw material until melting and working.
The glass making belongs to an extremely old technology, the history of which has not completely unravelled. Starting from 1st century AD, semifinished glass produced in the Eastern countries, by the so-called "primary workshops" (glass-making), were sent to the "secondary workshops" in Western countries, where a further stage (glass melting) was accompanied by a fining process leading to production of worked glass ((Foy and Jézégou, 1996, 1997; Foy et al., 1998, con biblio).

In the glass history, two compositionally different glass productions succeeded: until the Carolingian times, glass making in the Mediterranean and Central Europe was dominated by Na-Ca glass. The switch from Na-Ca glass to K-Ca glass represents a change of production technology, related to both raw materials availability and working methods.
Significant information about raw material provenance and firing technology can be derived from the analysis of of the unearthed remains of various stages of the productive cycle, such as glass sherds, frits, slag, fragments of crucibles (Casellato et al., 2003). The materials pertaining to the intermediate phases of a given production cycle are characterized by the occurrence of textural and compositional heterogeneities at different observation scales. A detailed textural and microchemical study of these heterogeneities (Messiga and Riccardi, 2001) can give information on provenance of raw materials, added components, efficiency of the melting process, liquid immiscibility, refining processing and cooling rate of glassy products.
Scientific studies on glass mostly concern fragments from Northern Europe and the Eastern Mediterranean, whereas less attention has been paid to finds in Italy, especially of protohistoric glass (Mirti et al., 2001; Verità et al., 2002 and references in it reported).

Archaeological glass findings still needs careful and systematic analyses. Despite a great number of roman artefacts analysed, the comparison between different compositional data are uneasy because the differences in analytical procedures (Mass, 1999; Brill, 1999).
In the Aquileia area some problem concerning the availability of silica component and the compositional constancy of the raw materials (sand and natron) (I cent. B.C. to VII cent. A.D.) remain still unsolved.
Colour is an important glass characteristic that mainly depends on the occurrence of transition metallic elements, on their oxidation state and electronic configuration. Actually, many factors, some of they are still not completely understood, are considered (Bamford, 1977; Newton, 1978; Cable, 1998; Doremus, 1994; Barber and Freestone, 1990).
Chemical, morphological, micro-textural and geochemical characterisation of alteration of Iulia Felix glass specimens evidence close relationships between glass chemical composition and alteration morphologies (Silvestri et al., 2004). Oxygen isotope analysis was also performed (Longinelli et al., 2004). This analytical approach is essential for understanding alteration processes, and for planning preservation and restoration strategies.

TASK -2- One of the major problems in the studies of ancient materials is the lack of reliable analytical standards. To analyse materials inhomogeneous, such as in alloys and glassy materials (glasses and glazes), concomitant microchemical and microstructural studies are of fundamental importance.

In the field of cultural heritage different analytical approaches have been rapidly introduced in the last years, consequently the lack of analytical standards is not easy to be solved, especially within a single research project, but surely deserves attention.
The present state of the art is that every laboratory has its own "internal" standards, so that there is no exchange or sharing of standards. Besides analytical standards, no standard sampling methodology has been defined upon yet, especially with regard to micro sampling (the only possibility when dealing with valuable historical artefacts). Another essential aspect to consider in dealing with inhomogeneous materials, such as those studied in the present project, is the definition of the microscale process indicators based on the interpretation of microtextures. Recently, on glass studies, an innovative and coherent definition of production and working indicators, at the macro-scale, has been proposed by Casellato et al., 2003: the shapes of different findings are associated to different stages of the production cycle of artefacts and to the different actions performed by craftsmen.
Much still needs to be done in the definition and standardisation of the microscale process indicators, especially in materials produced by the "fire-technology", such as those studied in this project. Infact in order to link microstructures to production processes it is necessary to perform a long series of logical and analytical steps, starting from a sound observation (sampling, textural analysis), up to direct experimentation and setting up of experimental runs. From end to end, are relevant the experimental studies on composition and textures of findings in order to reconstruct production processes and to define pertinent phase diagrams. Such a task cannot be run by a single research unit but requires a common effort, thus representing unifying means within the project, to which all RU cooperate. Principal outcome of this action will be the production of a "photographic atlas"of microstructures interpreted in the light of the production process from which they derived.
This work will lead to the production of a database with all textural and compositional data, implementing one already present in Siena (Gliozzo et al., 2002). It will be an integrated database where analytical and textural data will be linked to archaeological and historical ones, it will be used by a wide spectrum of scientists and archaeologists

TASK -3- In the field of ceramics, a well-established tradition of studies has revealed the importance of the introduction in the western Mediterranean, particularly in Italy, of new glazes coatings, that occurred between the end of the 12th and the first half of the 13th centuries (Berti et al., 1997). This followed the arrival, in the 10th century, of large quantities of glazed ceramics imported from Islamic (enamelled) and Byzantine (slipped) areas, which created an environment favourable to innovation. Skilled artists brought changes to the whole productive cycle.
Until now, the archaeometric studies mainly focussed on the reconstruction of the production technology (see Tite et al. for an exhaustive bibliography), that is to recognize the raw material, to define the conditions (T and kiln-atmosphere) during firing, to identify the pigments in the enamel decorations by using micro-Raman spectroscopy (Colomban et al., 2001).
Very few are the papers dealing with the study of interaction between glaze and ceramic body. The comprehension of this process can give useful information about production process, with particular regard to the modalities of application of the glaze. In fact, it is not yet well understood if the glaze was applied over the air-dried ceramic body or after a first firing (Tite et al., 1998), which was the duration of the second firing, if any, (Mason et al., 2001; Freestone, 2002), which factors affect the reactions between glaze and ceramic body (Molera et al., 2001).

The verification and modelling of glaze-body interactions are not clearly defined yet as well. The chemical composition which may be determined on a finished finding is the result of transformations in the starting mixture and glaze-body interactions (Molera et al., 2001).
It is therefore necessary to investigate these materials also by punctual analytical techniques. This techniques will allow to observe and, possibly, quantify the evidence of compositional and textural inhomogeneities. These inhomogeneities, probably due to a low efficiency of the production process, can supply meaningful information both about raw material use and production process. This kind of research could allow realizing process standards, that is a very innovative issue.

TASK 4 - In the reconstruction of the technology history, metals bear an important role (Tylecote, 1992; Giardino, 1998). The archaeometric investigation concerns morphological, structural, textural and compositional studies of complex alloys such as bronze (Tylecote, 1992; Bachman, 1982) and irons objects (Serneels, 1993; Heimann et al., 1998; 2001), as well as the studies of slags, furnaces remains and crucibles (Morton & Wingrove, 1969, 1971). It may provide further inputs to document and reconstruct the Mediterranean trade routes during different epochs, as well as within different cultural contexts (Gale et al.,1999; Woodhead et al.,1999; Zhu et al.,2000), such as the areas being studied by our Working Group: the Veneto Plain and the "Etruria Mineraria" (Gale et al., 1999; Woodhead et al., 1999; Zhu et al., 2000).
Systematic investigation of metal artefacts and slags are needed for the archaeological sites of Frattesina di Fratta Polesine, Terramare of western Emilia and Populonia, all sites were ascribed to a period between the IX century B.C. and the I-II centuries A.D.,
The most important European archaeological phenomena developed during the II millennium B.C.: the Bronze age which is attested by the Terramare, characteristic settlements in central western Emilia. These have provided an impressive amount of archaeological remains, including a substantial quantity of bronze artefacts and a significant volume of tools used for the handicraft production, as testimony of their production in loco (Bernabò Brea et al., 1997; Carancini, 1997; Cardarelli, 1997). The scientific question that is posed is to establish the provenance of the raw materials.
Archaeological and archaeometrical research has achieved excellent results. However, the question about the sources of raw materials and processing of artefacts is more complicated, bearing out larger areas of uncertainty. In the terramare the production of bronze objects indicate a widespread distribution of metal production, including areas distant from mineral resources.
A multi-tracer approach, based on trace element distribution and Pb- and Cu-isotope composition, is believed to represent a suitable tool for provenance reasoning. In particular, isotope analysis based on copper stable isotopes (65Cu and 63Cu), using a method still at the development stage, may provide further inputs to document and reconstruct the Mediterranean trade routes during different epochs and cultural contexts (Gale et al., 1999; Woodhead et al., 1999; Zhu et al., 2000).
As regards the processing of artefacts, significant indications may be inferred from the microstructures of the alloy. The metallographic analyses give good results, however, they are limited to the superficial portions of the various objects (upon removal of the weathering patina), or require a very invasive sampling. Recently, the development of X-ray and neutron diffraction techniques gives the possibility to obtain non-invasive microstructural analyses of the inner portions of the artefacts (Artioli et al., 2003; Rinaldi et al., 2004). With neutron sources, Cu-Sn compositional analyses may be also obtained from the alloy cell-parameters.

TASK - 5. At present, the mechanisms leading to the inhomogeneities observed in worked and semifinished glass, produced by pre-industrial technology, is in need of comprehension. Such inhomogeneities can be descrided as folded compositionally distinct ribbons and filamentous textures. Globular elements occur when the stretching and folding processes (during working) have not been applied. Glass of these textures show different compositions that testify incomplete homogenisation of melted materials. The mechanisms responsible of these microtextures and the interpretation of compositional differences are hypothetic and they should be verified through detailed investigations and reological modeling.
In ancient glass production, the recycling of cullets even if testified by historical evidences (Sternini, 1995), it's insufficiently demonstrated by analytical evidences, owing to the absence of a model that describes, in a dynamic way, the compositional changes induced by cullets to the melted mass. The convective flow within the molten glass is the dynamic force that, added to the chemical potential gradients, homogenises the melt.
The comparison between numerical models and analyses coupling classical petrological methods and the techniques of Chaos Theory and Fractal Geometry yield a remarkable improvement of the knowledge of the complex mechanisms that act during mixing of silicatic melts (Perugini et al., 2002; Perugini et al., 2003). In particular, it has been possible to reconstruct: i) dynamics acting during interaction; ii) the relative times of mixing in the various dynamic regions; iii) initial proportions of the end-members of the mixing process; iv) intensity of the mixing process. Reconstruction of all these characteristics is fundamental to tackle the archeometric problem of the production of glasses of preindustrial age.
A new possible field to be explored is the application of the models derived from ancient materials studies to improve present-day industrial productions. <<<