Using ATR-FTIR, analytical colour and mercury for unravelling the cremation ritual of Tyresta viking age burial mound (South-Central Sweden)

The funerary rituals in Viking Age Scandinavia are known by their complexity and diversity including inhumation, boat burials, and cremation. Cremations have been extensively studied macroscopically, but the application of geochemical techniques, although highly informative to investigate cremation in more detail, have not been widely explored yet. In the Viking Age the inclusion of both animals and humans on the funeral pyres makes research challenging. In the present study, we demonstrate the usefulness of molecular analysis (ATR-FTIR), direct mercury analysis (DMA) and analytical colour (in the CIELab space) for the characterization of Viking Age cremated remains of a human individual buried with dogs, a horse, a cat, and other animals – as well as evaluate macroscopic methods for assessing the temperature of burning. We demonstrate that the spectroscopic signal is highly correlated with analytical colour parameters, and with mercury concentration (still present in bones exposed at high temperatures). Mercury concentration was higher in human bones than animals’, suggesting an ante-mortem exposure. Human bones were probably heated at temperatures between 900 and 1100 °C, while animals were cremated at lower temperature. We also identified a secondary cremation in a layer previously interpreted as a badger burrow. A new Mid Infrared index (MIR-index, _T PV), is proposed, and we suggest that the cyanamide band is related to oxygen availability during burning. For the macroscopic method, we recommend splitting the white colour category into two based on bone porosity, to better qualify higher temperatures.