The term ‘organic residues’ is used to describe a range of amorphous organic remains from diverse natural sources, associated with a variety of artefacts found at archaeological sites. Most commonly, these are invisible, such as animal fats which have remained entrapped in the ceramic matrix during cooking, but they can also be visible, such as charred crusts.
Lipids are the fats, waxes and resins of the natural world. They are the most frequently recovered biomolecules from archaeological sites, for they can endure, often over long timescales, at their site of deposition.
- Terrestrial animal carcass (meat) fats, including distinction between ruminant (cattle/sheep/goat) and non-ruminant animals (e.g. pigs)
- Dairy fats
- Aquatic fats, including fish, shellfish and mammals, both ocean-dwelling and freshwater
- Plant oils
- Waxes, such as beeswax or plant waxes
- Resins, tars and pitches
ORA is generally known for its role in identifying what food products were processed or stored in ancient vessels. However, it can also address wider questions around the following topics:
- The manufacture, decoration and repair of vessels – for instance, the presence of adhesives or waterproofing agents
- Investigating the use of different vessel shapes
- Spatial patterning and activity-specific (for example pottery associated with different structures or activities/ritual practices)
- Food preparation techniques
- Resource exploitation, trade and exchange
- Ancient technologies – for instance, the composition and use of hafting materials, adhesives or balms
- Domestication of plants and animals – for instance the adoption of secondary products from animals
- Changes in diet and subsistence over time (for assemblages spanning multiple phases)
The research questions to be addressed will steer the number and type of samples required. The ORA team offers a complementary sampling advice service, where you will meet with our ORA specialist to guide you through your unique sampling strategy.
Although the sampled piece is only about 2-3 g, we usually require sherds of approximately 10 g or larger. This enables us to clean the sampled area effectively before it is removed from the larger sherd. We may be able to use smaller samples and smaller sherds in specific circumstances, this can be discussed with our ORA specialist.
Carbonised, or crusted, residues are usually more highly concentrated with lipids, and therefore the team would not need as much as 10 g of pottery when analysing this kind of sample. Our ORA specialist will provide bespoke advice based on your particular samples and context.
If sampling directly from site, it is preferable that the sample is not washed. However, if sampling from existing museum collections, it is likely that the potsherds will already have been cleaned. It should be noted that excellent results have been obtained from numerous cleaned potsherds from assemblages obtained from museum collections, therefore this should not preclude sampling from existing collections.
We are able to analyse pottery that has been stored in museums for tens of years as well as newly excavated sherds. Sherds stored for a long time, may or may not contain contamination, and for most of them, we will be able to detect the contaminators and carry on with the analyses anyway.
For all material, if possible, avoid (further) direct contact with plastic or cling film. As far as possible, try to avoid handling the sherds. If available, use nitrile (powder-free) gloves to handle the sherds. If gloves are not available, wash hands before sampling to reduce contamination by skin lipids and cosmetic products. Keep samples away from modern contaminants such as your coffee, lunch, suntan lotion etc.
For newly excavated material, avoid washing sherds or applying substances such as glues, consolidants or varnishes such as paraloid to sherds intended for organic residue analyses. Air dry sherds once lifted from the burial environment, wrap in aluminium foil (or acid-free tissue paper) and place in brown paper envelopes or ziplock plastic bags if site conditions are wet. Once wrapped, store the sherds in boxes.
Our team will ask for a brief account of the nature and history of the site, the aims and objectives of the project, and as much detail as you can provide regarding the samples (site, find number, context, pottery type, fabric) and the preservation/storage environment.
If you have quite specific research questions that ORA can address, then fewer sherds can sometimes provide adequate material. The sherds should be selected in consultation with our team, who will advise on how to maximise the research potential.
The technique requires grinding the ceramic sherds to powder to extract lipids. Therefore, it is, by necessity, destructive. However, only a small portion of pottery is required, and any sherd remaining after sampling can be returned, if required. Please do contact us if you are hoping to work on complete, near complete or special vessels, and we will be able to advise on the least destructive sampling strategy.
If possible, rim sherds are usually preferred for analysis, as research has shown that the rims of vessels tend to accumulate larger concentrations of lipids.
The time required to analyse samples will depend on various factors, including the number of samples, the specific techniques required for their analysis, contamination levels and time period of the assemblage. The analyses are quite lengthy and may take several months, but we will identify a timescale and a reporting deadline with you from the outset.
Yes, organic residues can survive well in conditions such as acidic soils that are not conducive to the survival of other types of organic material, such as bone. ORA can act as a proxy for animal husbandry where there are limited zooarchaeological remains and provide crucial and viable evidence where other organic remains do not survive, including the potential to yield radiocarbon dateable-material.
Yes, ORA can be performed on any unglazed ceramics, whether from prehistory or the historical period. Where available, historical records can provide a line of complementary evidence alongside other archaeological evidence.
Organic residue analysis is not one analysis, but can involve complex sample preparation steps and multiple instrumental analyses depending upon the question being asked and material(s) being analysed. Therefore, the cost per sample can vary depending on which types of analysis are carried out. Please do contact us for an initial quotation.
We welcome collaboration on larger, as well as smaller, projects. However, large projects are most successfully carried out as a research collaboration. Please do contact us about this, as we can work with you to determine the best strategy for your project.
Eligible UK organisations and individuals can apply to use our facilities funded through the AHRC RICHeS programme. Please see the HSDS catalogue of services for an overview of the wider range of services we can offer.