J Archaeol Sci 34 (10)

A variety of microfossils, originating from plant foods, become trapped in the dental calculus matrix. Processing of dental calculus allows extraction of these microfossils. The resulting data can be used to reconstruct diet at the individual and population levels as the identification of microfossils like starch grains and phytoliths to the generic level, and sometimes to the species level, is possible. However, in some archaeological sites, dental calculus deposits do not preserve well enough to be processed. To prevent the loss of information in such cases, the authors present a technique, called `dental wash'. It permits extracting microfossils from cryptic dental calculus deposits. In the two experimental archaeological cases presented herein the authors identified phytoliths, starch grains as well as a diatom fragment with this method, whereas in a control sample no microfossils were found. Moderate damage to the teeth was detected when they were already friable due to poor preservation. Minor damage to the surface of well-preserved teeth was observed. This indicates that the proposed method is efficient in recovering microfossils, but unacceptable because of damage to teeth. It is suggested that if the method could be refined, it would expand the potential of dental calculus analysis to a greater range of archaeological sites.

The authors demonstrate that NMR is an useful analytical tool to characterize rapidly samples of conserved wooden objects. By choosing an appropriate value of the contact time (from 3 to 5 ms) for which the PEG component gives only a small residual NMR signal in the CP-MAS experiment, it is possible to edit selectively the spectra of the wood components. It allows one to visualize the degradation extent of the archaeological wood even when the conservation processes have been already applied. Moreover, by studying the kinetics of CP-MAS experiments, the time constants, T1ρH and TCH values for PEG moiety were computed. From these data, it is shown that either in the crude commercial product or incorporated in archaeological woods, two components are present and they are the signatures of crystalline (or ordered) and amorphous (or disordered) molecular domains. Moreover, it was shown in the archaeological woods that almost 30% of PEG was in close molecular interactions with lignins. The study is evidence that the PEG in conserved wood can interact at a molecular level with wood components. It also demonstrates that the PEG diffuses inside the residual cell walls of archaeological wood.

New field and laboratory work was carried out on two vitrified forts, Rhubh Aird Ghamhsgail near Arisaig and The Torr near Acharacle. Fieldwork confirms that both are constructed from rubble largely comprising local psammitic Moine Supergroup rocks and that their walls are relatively well preserved with large portions of vitrified material remain, particularly at The Torr, where remnants of up to four courses of stone facing occur. The preserved wall fills comprise mostly psammitic rubble set in a dark brown, vesicular, glassy to aphanitic matrix that in many places preserves evidence of downward flow. Conventionally, vitrification is explained through combustion of timber interlacing within the walls leading to melting that has been modelled in the granite system. However, considering Iron Age smelting technology, this leads to problems in obtaining high temperatures (≥1000 °C) over tens of metres of wall length. Geochemical analysis of the vitrification indicates that modelling the melting within the granite system is incapable of providing a partial melt matching the composition of vitrification. At The Torr, pelite fragments have been found near the base of the wall where partial melt occurs as black bubbles. In these fragments it appears that micas (largely biotite) have formed the melt via the reaction biotite + quartz = sanidine + orthopyroxene + liquid which takes place at temperatures c. 850 °C. Quench crystals in the melt include orthopyroxene, plagioclase, spinels, ilmenite, magnetite, anatase and apatite confirming that it was not a granite melt. These melted fragments are found next to material with biotite that, superficially, appears unmelted, suggesting that some of the heating took place perhaps away from the edifice and unmelted residue was utilised as part of the rubble fill, suggesting that in situ partial melting of the rubble is unlikely. However, in other parts of the edifice heat affected, yet unmelted, fragments are dominant. The new evidence indicates that vitrification occurred at lower temperatures than previously modelled and thus the melts could have been achieved more easily than previously thought.

A sample of eleven museum artefacts was examined to assess the preservation of any adhering organic residues, particularly starch granules, and to assess the potential for the identification of cooked starchy foods. The primary aim was to examine starchy deposits, extract starch granules and examine their physical condition to increase our understanding of the taphonomy of starch granules and associated organic residues in archived material and archaeological deposits. The study shows that organic plant residues could be recovered from archived artefacts and makes a significant contribution to understanding the function of this material. Recovered starch granules showed an interesting pattern of varying organic preservation on the surface of stone and wooden artefacts. Some starch granules were found to be well preserved while others in the same sample appeared to have been affected by enzyme degrading micro-organisms. Recovered residues included fully gelatinised starch.