3.6 Lithics

Lithics have offered many opportunities for materials analysis. In the work on identifying and sourcing a range of lithics (Table 5), geological reconnaissance in the field is essential as the investigations of sandstone, pitchstone and steatite (soapstone) have shown. Miller and Ruckley (2005) and Miller et al. (2006) identifed the stones, mainly sandstones, used in a large number of Pictish and West Highland sculpture; their approach was perforce non-destructive (Table 5), combined with magnetic susceptibility measurements which were able to refine the stones’ basic petrographic classification. In the case of studies requiring a sample to be taken for elemental or other analysis, two points stand out: (a) inter-source discrimination usually demands that the analytical technique be capable of determining with high precision the relevant elements present at very low concentration; this was the case for steatite/soapstone from some of the main quarries on Shetland and in Norway which could be differentiated on the basis of rare earth element compositions; (b) intra-source variation in composition also has to be considered.

Flint and chert deserve comment as the prominence they hold as artefacts in Scotland has not been shared by progress in investigating their sources by science-based methods.   The compilation of sources throughout northern Britain, begun by Wickham-Jones and Collins’ (1978), has been supplemented by more geographically focused prospection, for example on Islay, Colonsay and Iona (Marshall 2001).  The approach of chemical characterisation of flint axes and known prehistoric flint mines in the chalk environment of southern  England (de Sieveking et al  1972) appears less applicable to the Scottish situation because many flint occurrences are with gravels and thus are not only secondary but could also be mixed;  instead the palynological approach may offer scope to judge from Harding et al’s (2004) identification of over sixty species of dinocyst and other types of microplankton in flint nodules from Islay.   Owen et al’s (1999) chemical characterisation of chert in the Southern Uplands is promising although the results are as yet insufficiently fine-grained to be used for archaeological purposes.

Apart from issues of identification and sourcing of stone in Scottish buildings and monuments, both ancient and more recent, there is the continuing need for research in heritage science. Historic Scotland’s Conservation Department, which is at the forefront of this effort, supports a range of work, as well as having its own science-based facilities. Historic Scotland (2011) has compiled a list of its own publications on conservation: Technical Advice Notes (TANs), Inform Guides, Research/Study Reports, Technical Papers, Guide for Practitioners, Case Studies, Technical Reference and Guidance Manuals and Reference Reports. The TANs deserve special reference for their wide-ranging topics, from the quarries of Scotland (McMillan et al. 2006), to specific stone types such as slate (Walsh 2000), building stones of Edinburgh (McMillan et al. 1999), earth structures and construction (Walker and McGregor 1996), maintenance and repair of cleaned stone buildings (Young et al. 2003; for Edinburgh see also Hyslop 2004) and Scottish stone used in Ireland (Curran 2010). Charlestown Consultants, part of the Scottish Lime Centre, also have such facilities, specialising in the analysis and evaluation of mortars (Scottish Lime Centre 2003), plasters and renders. Critical to the understanding of decay processes and determining preservation strategies is knowledge about moisture transport and the formation/movement of salts within stone and mortar studies. There have been studies at Skara Brae (Hamilton 2006) and more recently work relating to mortar and concrete render (Griffin et al. 2010).