Determining the Sr isotopic composition of waterlogged wood – Cleaning more is not always better

Sr isotopes represent a potential means to trace the provenance of archaeological timber. Such tracing allows us to examine the transport, by past people, of wooden objects and of wood and timber as a raw material. However, issues exist with the mobility of Sr and addition of exogenous Sr during waterlogging. This paper presents a systematic assessment of cleaning methods to remove exogeneous Sr from waterlogged wood. Neither a large number of Milli-Q washes, a combination of MQ and Hydrofluoric acid (HF) or alpha-cellulose extraction were able to retrieve the original signature. It was also shown that ashing leads to higher uncertainties due to the smaller amount of Sr available for analysis, this method will only be really useful when large samples are available, is not recommended for small archaeological samples. Our studies also highlight that the distribution of Sr in waterlogged wood is highly heterogeneous.