Complementary analysis to de-convolute co-located contaminants in marine archaeological bricks

Abstract

• Using complimentary analysis to de-convolute complex heritage materials. • Determining the elemental composition of compounds in marine archaeological bricks. • Synchrotron techniques for phase composition of complex archaeological materials. • Understanding the threat posed by compounds present in marine archaeological bricks. Marine archaeological artefacts contain unexpected compounds due to prolonged exposure to the sea. These can remain dormant and embedded within materials until a change in their surrounding environment, such as exposure to oxygen, prompts a transformation. These changes can pose a problem, as acidic compounds are formed which disintegrate the material, or crystals form which physically break the artefact apart. The extent of these transformations is highly heterogeneous due to its dependence on the ability for oxygen to reach and catalyse these reactions. Additionally, these transformations are heavily dependent on the environment the artefact is exposed to, and the pathways available for ingress, either naturally or through previous degradation. This results in materials with a range of different compounds which are often co-located on the macro, micro and nano-scale. Trying to de-convolute these compounds is challenging, and usually requires a suite of complementary techniques to achieve. Here we report on damaging salts found within marine archaeological bricks and show how it is only possible to qualitatively and quantitatively understand what is present by employing a range of analytical techniques, such as XRD, SEM-EDS and SR-XPD. The marine archaeological bricks studied were found to contain a range of different sulfate-based salts, which had grown crystals in preferred orientations. This provides information which will guide further conservation strategies such as how these bricks are stored, conserved and protected in the future. (a) The galley of the Mary Rose (b) salt samples located on and within the bricks (c) SEM analysis of the salts present (d) demonstration of the enhanced data quality of synchrotron XRD compared to laboratory based instruments.