Identifying the “blue substance” at the Roman site of Vindolanda, Northumberland

Archaeological landscapes and environments are extremely complex and diverse systems. Vindolanda, situated in Northumberland, UK, is part of the Frontiers of the Roman Empire World Heritage site and has remarkable preservation of artefacts of international significance including leather, writing tablets and bones. Vindolanda is a waterlogged site and contains anoxic layers which, it is postulated, aids in the preservation of these important artefacts. The anoxic layers contain many chemical and microbiological properties which vary from context to context, depending on what remains in the soil and what is introduced into the archaeological environment through continued post-depositional processes. During excavations at Vindolanda, as at other sites the presence of a ‘blue substance’ has been noted by researchers for many years. This ‘blue substance’ has been generally described in the literature as Vivianite (hydrated iron (II) phosphate), and has speculatively been used as a signature of good organic preservation in archaeological contexts. In this paper, a range of analytical instrumentation SEM-EDX and XRD has been used to characterise the blue substance, taken from one well defined context to confirm as Vivianite (Fe ₃ (PO ₄ ) ₂ ·8H ₂ O).