The unburied reference collection, consisting of the same twelve residue types and control flakes used in the experimental groups, was created and studied prior to analysis of the buried material. Residues were known to be present on the flakes and could be seen with the naked eye. The flakes were stored in a refrigerator at 5°C, except during imaging with SEM when they were kept sealed in individual containers with silica gel desiccant. Reference collection residues in a fresh unaltered state were analysed with visual characteristics documented. This image library formed the basis for interpreting experimentally degraded residues. As with the buried pieces, VLM and SEM micrographs were collected for the twelve residue types in the reference collection, as well as the blank stone material.
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