The Gold Standard of Archaeology | Residue Contamination, Conservation Treatments and Chemical Attribution

1. Detection and attribution are different claims

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A chromatogram, spectrum or micrograph can support the presence of a compound, element or structure. It does not by itself establish when the material arrived or which activity produced it.

Write the inference chain in stages: signal, compound class, source candidates, pathway to the artefact and archaeological interpretation. Each stage needs its own evidence and uncertainty. “Detected protein” is not equivalent to “this tool butchered deer.”

2. Reconstruct the object’s full contact history

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An artefact moves through use, discard, burial, excavation, washing, labelling, packing, storage, conservation, display and sampling. Soil, hands, bags, marker inks, glues, consolidants, cleaning agents and laboratory surfaces can all contribute material.

Create a contact-history timeline from field notes, conservation records, packaging labels and staff knowledge. Unknown steps are not blank evidence; they are uncertainty that limits attribution.

3. Separate ancient background from modern contamination

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Residues can be unrelated to human use without being modern. Plant roots, microbes, groundwater, sediment and contact with other materials may deposit or transform compounds during burial.

Modern contamination begins after recovery but can be chemically subtle. The useful comparison is therefore not simply ancient versus modern. It is use-related, burial-related, excavation-related, conservation-related and laboratory-related pathways.

4. Design a hierarchy of blanks and controls

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A solvent blank checks the analytical run. A laboratory procedural blank follows preparation without archaeological material. A field blank samples excavation and packaging conditions. Sediment controls test the burial background. Material controls can test bags, labels, adhesives or consolidants.

One clean blank cannot exclude every route. Choose controls that correspond to the claimed pathway and process them with comparable timing, reagents and instruments.

5. Treat conservation products as part of the chemistry

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Adhesives and consolidants can introduce resins, solvents, plasticisers and additives. Cleaning can remove original material or redistribute later material. A treatment that stabilises an object may reduce its suitability for a future analysis.

Record product name, manufacturer, batch if available, solvent, concentration, application area and date. When formulations are proprietary or changed over time, obtain reference material where possible and report the uncertainty.

6. Worked example: compare candidate pathways

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A stone tool yields a resin-like marker peak of 120 units. The sediment control is 8, the procedural blank 3, an untreated comparison artefact 14 and a sample of the museum consolidant 110 with three matching secondary peaks. A second area of the tool, documented as untreated, measures 16.

The strong match and spatial pattern make conservation product the leading explanation. Subtracting 3 from 120 does not rescue an ancient-resin claim because contamination is not a uniform background. The report retains the detection but rejects ancient attribution for the treated area.

7. Use multiple features, not one familiar peak

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Chemical attribution strengthens when retention time, several diagnostic ions, isotope values, molecular ratios, spatial distribution and archaeological context converge. A single peak can be shared by several materials or created through degradation.

Compare against authentic and procedural reference materials with the same instrument and preparation. State whether the evidence identifies a compound, a source class or a specific organism. Those are different levels of certainty.

8. Changed-context transfer check

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Move the worked example from a conserved stone tool to pottery excavated recently with no museum treatment. The need for a pathway map and controls transfers. The likely sources change: gloves, plastic bags, soil lipids, handling and laboratory reagents become more important.

A sediment control now has greater value, while a consolidant reference may be irrelevant. Transfer the control logic, not the original contaminant list.

9. Limits and common misconceptions

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A blank below detection does not prove the artefact was uncontaminated. A contaminant can be localised, introduced before the blank existed or absent from the sampled control. Conversely, finding a modern compound does not mean every residue is modern.

Do not clean first and document later. Do not assume “archival” products are chemically invisible. Do not identify species or behaviour from a non-specific compound class. Destructive sampling cannot be repeated indefinitely.

10. Audit sampling, custody and interpretation

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Check provenance, field handling, conservation, storage, sampling location, tool cleaning, staff changes, reagent lots, blanks, instrument sequence, raw files and reference libraries. Photograph the sampled area before and after removal.

Re-run a subset with reordered samples or another method when carryover is plausible. Archive spectra and decision rules, not only a final label. The audit should let a later analyst distinguish absence of evidence from absence of documentation.

11. Frequently asked questions

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Can an untreated-looking artefact still be conserved?

Yes. Consolidants can be visually subtle and treatment records incomplete. Inspect under appropriate methods and check documentation.

Should the blank value be subtracted from every sample?

Not automatically. Subtraction assumes a stable additive background; localised or pathway-specific contamination needs a different interpretation.

Does matching a modern product prove contamination?

It can strongly support it when multiple features and the contact history agree, but report the specificity and alternative sources.

12. The gold standard attributes a pathway, not just a signal

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Residue claims become archaeological when chemistry, context and custody tell a coherent story. Sensitive detection is the beginning of that story, not its conclusion.

Before assigning an ancient source, ask which control represents each later contact, what evidence distinguishes source candidates and whether the claim would survive if the treatment history were discovered tomorrow.