As a work of archaeological science, this study embodies a number of theoretical assumptions concerning the manner in which ancient materials are studied and interpreted. The theoretical understanding of X-ray techniques and their practical application to archaeological samples are discussed at some length in Chapter 4. Here the concepts underpinning the application of analytical techniques to the study of archaeological material are briefly considered. In this context the term “archaeological science” is simply used as a term to describe the application of methodologies developed by the physical sciences to ancient materials, rather than to lay claim to “scientific” status for the elaboration of wider inferences
concerning the societies using the materials (Trigger 1988, p 1 and 1989, p 373- 374).
The chemical analysis of ancient glass dates back to the late 18th and early 19th Centuries (Caley 1949, 1962, p 13 – 15, 1967, p 120), with the curiosity of early chemists driven, in part at least, to understand the technologies of the classical world to facilitate the production of contemporary materials. Amongst the justification for the investigation of “the nature and composition” of a range of pigments and vitreous materials from Pompeii, Humphrey Davy suggested to his audience
“I shall be able to give some information not without interest to scientific men as well as to artists, and not wholly devoid of practical applications” (Davy 1815, p 99-100).
It is interesting to note Davy’s ethical approach to the sampling of the materials: “When preservation of a work of art was concerned, I made my researches upon mere atoms of the colour, taken from a place where the loss was imperceptible: and without having injured any of the precious remains of antiquity” (Davy 1815, p 100).
It wasn’t until later in the 19th Century that an explicit statement of the value of chemical analysis for the resolution of specifically archaeological questions was made. In the preface to the 1879 edition of his book (Manufacturing Arts in Ancient Times, with special reference to Bible History), James Napier discussed the origin of the dead and their grave goods from excavations at Mycenae:
“I think it probable that if chemistry was called in as evidence in such enquiries, it would at least, yield much valuable circumstantial, if not positive evidence as to whether the articles found alongside the bodies
were of Grecian or Scandinavian manufacture…and I think that nations so far apart as the north of Europe and Greece may, and in all probability had, different methods of compounding their alloys; so that, were this the case, strict analyses of the different articles found would approximately
determine whether they were made in Greece or northern Europe. … With the knowledge which archaeologists have attained in respect to form and other characteristics of ancient works, I believe that, were analyses added to this knowledge, the archaeologist would soon come to determine not only the age, but the locality where the different articles were made.”
Napier concluded his preface with a call to arms for archaeological scientists: “As yet I think archaeologists have not put that value upon chemical investigation that it deserves, and hope that this volume will help to stimulate to such an enquiry.” (Napier 1879 p II-IV).
In the brief passage quoted above, Napier identifies a number of the key concerns of the chemical characterisation of ancient materials: identifying technological processes, technological traditions, the relationship to form, dating and
provenance.
The application of natural sciences to archaeological research has expanded hugely since Napier’s day, and extends to include such diverse areas as environmental reconstruction, paleopathology, biological evolution, dating, prospection and conservation science: nonetheless the compositional and
brief history of the development of archaeological science see Pollard and Heron 1996, p 1-19, and also: Caley 1951, 1962 and 1967, Brothwell and Higgs 1969, p 23-34, Harbottle 1982, Ciliberto 2000, and Brothwell and Pollard 2001b, p xvii- xx).
The value of an archaeological scientific investigation into any body of material is dependent on two key issues: the construction of a suitable archaeological
question and the selection and application of the appropriate analytical
technique(s) to the resolution of the question (the latter is considered in Chapter 4).
Clearly several assumptions are implicit in the chemical characterisation of a group of artefacts:
technological processes
technological tradition
grouping/association – difference provenance
It is useful to consider the limitations of these concepts for the purpose of this study. The manner in which glass artefacts may be studied is examined in greater detail in Chapter 3, but it is important to question the usefulness of certain objectives to interpretation. The chemical and structural examination of glass artefacts permits the detailed reconstruction of an object’s life history (or chaine operatoire –Tite 2000, xv-xvi, Tite 2001, p 443, Dobres and Hoffman 1994, p 237-239). Sufficient knowledge has been collectively accumulated by
archaeological scientists to infer distinct raw materials, temperature regimes, oxidation states, forming activities, use, re-use and depositional environments for glass artefacts. Whilst an understanding of these processes is a worthy end in itself, and not a new objective for archaeologists, it is the interpretative value placed upon technology which varies between archaeologists.
The examination of a glass artefact (or group of artefacts) permits its relation to the larger body of compositional and structural data: a large number of regional and temporally specific traditions have already been defined. Clearly, the quantity (and quality) of data in existence for a region and period determines the capacity for defining new analyses. For any particular period the categorisation improves with additional data, as the groupings become better defined (or redefined), for example the five glass compositional groups defined by Sayre and Smith in 1961 for Europe, Western asia and Africa from 1500 BC until 1200 AD has been greatly extended (Sayre and Smith 1961, p 1824).
The grouping of artefacts, and differentiation on the basis of shared traits is also a long established archaeological practise, since Thomson’s seriation in 1819 led to the definition of the Stone, Bronze and Iron Ages in European Prehistory (and their internal differentiation: Trigger 1988, p 1-2). The assumption that differences must exist between data sets from artefacts which are distinguished on other, archaeological grounds (such as form, association, context or date) is an eminently testable proposition in each case, using statistical techniques (e.g. Glascock 1992). The imposition of difference, using sophisticated statistical methodology is not
difficult, but groupings still need to be explained in terms of their technology, and related to their archaeological significance.
Provenance studies based on chemical characterisation of some archaeological materials have been very successful, with unequivocal identification of the geological source for certain types of artefact (for example obsidian: Henderson 2000, p 305-314, Pollard and Heron 1996, p 81-103, Wilson and Pollard 2001). Similarly ceramics have been successfully characterised and related to specific geological sources of clay (Pollard and Heron 1996, p 104-148). Glass however, represents a more fundamental re-working of quite diverse raw components, which makes the establishment of a relationship between the finished product and specific geological sources difficult if not impossible. An individual glass artefact might contain components with separate and distant geological origins (for example exotic colourants in locally-produced glass, also see 3.7 below). Glass as a material does not readily lend itself to provenancing, in the manner of stone or ceramic. The well-documented and archaeologically attested phenomenon of geographically distinct manufacture, colouring, working, and recycling of glass renders the concept of provenance redundant (Wilson and Pollard 2001, p 512- 513). However, the definition of technological tradition is in many ways more useful, for this can distinguish characteristics which might have a geologically specific aspect (such as a high-alumina cobalt colourant), alongside traits which are associated with raw component-selection which are less geographically dependant. The consideration of technical tradition also more readily permits the acknowledgement of culturally determined choice.