Introducing Organic Residue Analysis and Archaeology: Guidance for Good Practice
Julie Dunne
Richard Evershed
Dr Lucy Cramp
The authors introduce Historic England's 2017 guide to organic residue analysis and explain what this technique can bring to archaeology by identifying food remains and materials used in ancient manufacturing such as resins, tars and pitches.
Why we published the guidance now
In January 2017, Historic England published Organic Residue Analysis and Archaeology: Guidance for Good Practice. The time was right for this guidance – organic residue analysis is now a mature field of study, built on solid foundations of robust chemical concepts, backed up by experimental studies. Certainly, over the last twenty-five years, organic residue analysis of thousands of pottery sherds, excavated from sites across the world, have contributed considerably to our understanding of past people’s diet and subsistence, technology and resource acquisition/exploitation, amongst other questions.
We are now in a position, in the UK , where we can demonstrate both the extent of our knowledge at the site level through to broad scale questions regarding past economic practices and, significantly, where ‘gaps’ in our knowledge exist.
What the guidance sets out to do
The guidance booklet was written in partnership with a range of archaeological professionals, including local authority archaeology officers, archaeological units and consultants, project managers, curators, conservators and pottery specialists, and is designed to:
- Inform practicing archaeologists of the principles and potential applications of organic residue analysis (ORA)
- Provide clear and coherent guidance on organic residues recovery, sampling and analysis.
- Demonstrate the research potential of the approach
It should be noted that the majority of organic residue analyses are performed on absorbed residues from pottery, and these are the main focus of the guidance. Absorbed residues, comprising lipids (the fats, waxes and resins of the natural world), are preserved within the vessel wall. Comparison of their ‘chemical fingerprint’ to those found in modern organisms allows us to identify the commodities, such as meat, milk, fish and plant oils and waxes, processed in archaeological vessels. However, visible (or surface) residues adhering to pottery and amorphous residues (such as resins, tars and pitches) are also discussed.
What organic residue analysis can bring to an archaeological investigation
The primary aim was to emphasise what organic residue analysis can bring to an archaeological investigation. It seemed that most archaeological professionals (who had heard of the technique) know that ORA provides information on pottery function but the application to dietary reconstruction and, more broadly, subsistence practices, is less well-known. For example, ORA can identify the processing of animal commodities through the detection of carcass products from ruminants (cattle, sheep and goat) and non-ruminants (pig), as well as dairy products, fish, beeswax and, rarely, plant oils and waxes.
What seemed less well-known was the fact that the technique could be used to answer other archaeological questions, such as what materials were used to repair or decorate vessels and also to identify post-firing treatments.
A great example of relating form and function through ORA analysis is seen in the analysis of the lamps and ‘dripping dishes’ from the Causeway Lane excavation, Leicester. Compound-specific analyses of the fatty acids (C16:0 and C18:0) revealed the presence of ruminant animal fat (tallow), such as sheep, goat or cattle, in the lamps and non-ruminant animal fat, such as pig, was found in the ‘dripping dishes’, suggesting they were probably used as receptacles for fat collection during spit-roasting (Mottram et al 1999).
We felt that demonstrating the research potential of the technique would encourage practitioners to build organic residue analysis into their project budgets as its greatest value lies in its application at site level, which can ultimately feed into local and even regional assessments.
As with all project work, the key to successfully integrating scientific analysis into development projects is early and ongoing engagement between the organic residue and pottery specialists and the archaeologists, planners and developers, to ensure the sampling strategy maximises recovery potential. We’ve tried to provide lots of information on how to sample pottery for ORA, here, perhaps the most important message to get across is to have a clear idea of the archaeological question that you want the technique to address. This will dictate the sampling strategy, for example, number, type and context of samples required.
Quick reference
To make things simple and accessible the guidance has two tables which provide a comprehensive overview on the ORA technique and its applications.
The first table details what commodities ORA can identify, the chemical compounds (biomarkers) we use to identify them and the level of specificity that can be achieved. This simply means whether the commodity could be identified to species, for example, specific biomarkers identified the processing of Brassica oleracea (probably cabbage) in vessels at Saxon/Medieval West Cotton, Northamptonshire (Evershed et al. 1991). Further examples of specific commodity processing are supplied.
The second table describes what types of archaeological questions could be asked of the pottery at site level and what type/number of samples/assemblage would be required to investigate this. How these questions might fit within large-scale archaeological themes and examples of target periods/regions are then presented, and, finally, specific case-studies of these multi-layered applications are provided.
As an example, spatial patterning and vessel specialisation was identified in analyses of Late Neolithic Grooved Ware. These were preferentially associated with pig consumption, and furthermore, a clear connection between pottery from ceremonial sites and pig exploitation was made, suggesting a ritualistic aspect to pork consumption (Mukherjee et al. 2008).
A further example of both resource exploitation and trade and exchange was demonstrated by the use of resins in mortuary rites in Roman Britain, including coniferous resin, mastic and terebinth resin from the Mediterranean and frankincense from southern Arabia or eastern Africa. This provided valuable information on practical and symbolic aspects of Roman mortuary rites and into Britain’s relationship with the Roman Empire (Brettell et al. 2014, 2015).
Technical details
To keep the guidance document short and easy to read we placed much of the technical information into the online ‘supporting information’ document. This covers extensive detail on the science behind ORA including lipids, the analytical techniques used and preservation. We have consulted widely to provide some guidance on future ‘research agendas and strategy’ so that archaeological professionals have an idea of where ORA might usefully be targeted. A full glossary and details of further reading are also supplied.
