3.1 Introduction: Materials analysis

This large theme can be classified according to investigations into Technology, Provenance and Function. The theme also relates to issues in conservation science such as decay, stabilization and maintenance.

The following questions about materials are relevant to an understanding:

  • Identity of the material(s) from which the artefact was made?
  • Technology of fabrication of the artefact?
  • What was the source of the artefact or the raw materials?
  • What was the function and use of the artefact?
  • How has the condition of the artefact altered, or been altered, since antiquity?
  • What is the material condition and how can it be stabilised and preserved?

These questions are crucial because they concern such fundamental aspects of the past as technology, use, trade and exchange. Understanding materials also leads to more abstract but no less valuable insights into the past which are bound up with the issues of ideology, choice and value: was a particular material or production method used over another for social, practical or a combination of reasons?

Chronologically and typologically, artefacts are enormously wide ranging, from Neolithic pots to Iron Age torcs to Viking steatite bowls to silver coins, reflecting the spectrum of inorganic raw materials available in Scotland from the well-known metal ores, clays and building stones to more unusual ones such as Arran pitchstone. Artefacts of organic nature have very often been lost from the archaeological record, but materials such as bone, walrus ivory and whales' teeth (as in the Lewis chessmen), amber and jet are well known, and there are materials that are neither raw material nor artefact, for example cramp, a vitreous seaweed cremation ‘waste’ of prehistoric Orkney.

Equally, the scope and scale of investigations, adopting an array of science-based techniques and approaches, is very wide ranging. The age of the artefact or material of course holds no barrier to its examination. Some investigations are site-based, focusing on artefacts/materials deriving from recent archaeological excavation which pose questions of immediate concern and interest, sometimes in a conservation context, (eg. the Viking boat burial on Sanday (Owen and Dalland 1999). Other investigations may be concerned with an individual museum object, such as the Monymusk reliquary, or examples of a particular artefact type, such as brooches. Drawing on artefacts from several sites which are now housed in museum collections, other investigations have a wider remit, often extending beyond Scotland to a European or world-wide context (e.g. faience). There are enquiries that in going beyond the laboratory examination demand an experimental approach, for example pottery making, metal working and vitrified fort construction and firing.

Of equal relevance are items that are less archaeological in their status but instead are products of the visual and decorative arts, originally made to decorate a church, a palace or a home, such as paintings, textiles, furniture, metal and glassware, and now commonly exhibited in a museum or gallery. Here the enquiry may be more conservation based, but its outcome can have equal technological interest as well as providing information about the biography of the piece and the source of its raw materials. Into this category may belong sculpted stone, such as Pictish crosses.

The fundamental importance of analysis to many aspects of the conservation and long-term preservation of artefacts deserves further attention. Clearly it is important to know what the material being conserved is, while the identification of corrosion products and the understanding of degradation processes inform both conservation treatment and knowledge of the object history and past environments. In some cases the treatment has to be developed and monitored using scientific methods which may themselves be applied in a novel way to meet the particular demands of archaeological materials; the preservation of waterlogged wood being a good example of this. Conservation science is a specialist part of the application of science to heritage materials, but is often inextricably mixed with characterisation and study of fabrication technology; examples include the Forteviot Early Bronze Age dagger burial, the radiography of corroded ironwork to define preservation strategies, and understanding the effects of light damage on pigments or organic dyes.

Almost alone among the themes presented in this document, Understanding Materials usually operates within a context of specialisms that combine the traditional with science-based. One scenario sees the finds specialist, having identified questions that only a science-based analysis or examination can resolve, setting up a collaboration with one or more analysts. The success of that collaboration is as much a function of effective communication between specialists in optimising the interpretation of the scientific data as it is of the scientific data alone. In any case, the science-based analysis/examination is likely to involve more than one technique, beginning probably with one of the non-destructive techniques outlined below and leading to more detailed analyses requiring a sample to be taken. The same remarks apply to the reverse situation where the initiative is taken by the scientist/analyst leading to discussion with the museum curator or finds specialist on the historical or archaeological interpretation of the analysis/examination.

The techniques of analysis are numerous, reflecting the various purposes of investigations, as well as the likelihood that a given investigation will lead to the application of complimentary techniques to reveal further information. The three broad categories outlined below encompass the main techniques found to be applicable in Scottish work.

Non-destructive techniques

  • Optical, scanning electron microscopy and other surface visualisation and characterisation methods.
  • Radiographic methods using X-rays, neutrons and other penetrating radiation to reveal internal structures and compositional differences.
  • Elemental and chemical analysis using spectroscopic methods with infra red, visible and shorter wavelength light, synchrotron, X-rays and partical excitation.

Techniques requiring samples to be taken and preserved:

  • Spectroscopic and microscopic methods for petrographic, mineral and metallurgical analysis revealing crystalline structure and phase compositions, and technological examination of paint and other layers. Elemental analysis where sampling, for example, to fit into vacuum chamber.

Requiring samples or micro-samples to be taken and destroyed:

  • Spectroscopic and mass spectroscopic methods where molecular and isotopic information is obtained by dissolving or dissociating the sample in solution, vapour or plasma.
  • Chromatographic and combination methods to determine molecular structure and composition.

Petrographic analysis has a long history in identifying and sourcing stone types from historical and archaeological contexts in Scotland, but it is since the 1970s that the science-based component of understanding materials has accelerated. Mention should be made here of the early and pioneering analytical work on artefacts by Hugh McKerrell at the laboratory of the National Museum of Antiquities of Scotland (McKerrell 1974). Since then there have been many major advances in analytical methods, with equipment and techniques now available which can provide a wide range of analytical information on microscopic sized samples. The developments of analysis using synchrotron radiation and adaption of methods arising from the expansion in forensic science means that heritage science now has an often bewildering array of analytical methods potentially available, while at the same time the complexity of establishing, operating and maintaining such equipment means that it can only be supported and used in expensive and specialist centres. In the face of such opportunities it becomes increasingly important to ensure that the questions being asked/data being sought are well defined so that the most relevant and diagnostic outcome is obtained.

Methods of physical examination, are therefore numerous and rapidly changing as new methods and combinations of examination and analysis are developed; one important consequence of improved detectors and instrument design is the reduction in sample size. Many of these are well known techniques where the generation of results can almost be guaranteed. New methods and techniques are, however, constantly emerging where the success in,  or relevance to, any enquiry is less certain. To implement these may have an element of risk to the object or require precautionary sampling. The discipline needs to be open to this process, for example, in certain DNA and isotopic studies. Both

Related to this topic is a the ScARF Case Study: ‘Data Treatment and Interpretation’ on data treatment of analytical data which extends the account of Statistical Modelling in Archaeological Applications given in Section 1.6.

The UK National Heritage Science Strategy identified many of the issues relating to the discipline and illustrated the actual and potential public benefits arising from the understanding, preservation and enjoyment of heritage that it brings. The key strategic aims which the report draws together are as relevant to Scotland as to the rest of the UK. The examination of ancient materials and Conservation Science feature regularly in such public events as the Edinburgh Science Festival, but there are many more opportunities to engage with the public and increase recognition and support.

Partnerships are strong across the community in Scotland, but there remains plenty of scope to strengthen existing links and build new partnerships which will, it is hoped,  lead to the fuller availability of resources. There is a need to ensure that, through partnerships, collaborations, training and where possible enhanced funding, there is built a secure future capacity to match the growing demand for science based infrastructure to support archaeology and historical studies and preserve material for the future.