Identification of slates of Royal Cottage

Case Study

There is no single procedure used to identify used slates, but rather a combination of methods ranging from local knowledge to more scientific analyses . For a general discussion on the methods used see Identifcation of used slates  The identification of the slates of the Royal Cottage are just one example of the application of some of these methods.

View of the intake of Glasgow’s main water supply

The front of the Royal Cottage

Royal Cottage is situated on the south shore of Loch Katrine at Stronachlachar approximately 20km north-west of Aberfoyle.   Loch Katrine became the primary water source for the city of Glasgow and the surrounding area when in the middle of the19th century an aqueduct was built to transport water to the city. Construction of the aqueduct started under the supervision of James Watt and Thomas Telford and was completed in 1859 (www.incallander.co.uk accessed 08/01/2010). The Royal Cottage was built to accommodate Queen Victoria on the occasion of the inauguration of the aqueduct. However, she never actually stayed in the Cottage as the windows were shattered during the 21 gun salute. 

 In November 2009 the Scottish Stone Liaison Group requested that slates from the roof of the  Cottage be tested in order to establish their provenance.     Using XRD and trace element analyses (as described below), it was found that the slates were from one of Aberfoyle Group of quarries

The slates of the Royal Cottage

Methodology: The slates vary widely in thickness, width and length from which it was inferred that they are Scottish.  However the absence of pyrite crystals or crenulation of the surface excludes Ballachulish and Easdale slates. For these reasons, and substantiated by their grey-green colour, the source of the slates was identified as one of the Highland Boundary Group of quarries.   This Group consists of a series of quarries  located at intervals just north of the Highland Boundary line from Arran to Dunkeld (Scottish Slate Quarries 2000 J A Walsh, Publishers Historic Scotland). However, of these the most likely quarries are Luss and Aberfoyle which are the closest geographically and are known to have produced slates in the 19th  century.  

To distinguish between  slates from the different Highland Boundary quarries,  X-Ray Diffraction  (XRD) scans of the Royal Cottage slates were compared with those in the database. One  of the characteristics of the  XRD scans used in distinguishing between different Highland Boundary slates is the shape of the white mica peak (or peaks) at 9° 2 theta angle.  In some slates there is a double peak at this location due to the presence of the sodium-rich mica, brammulite in addition to the normal potassium-rich mineral     In Bute  slates this secondary peak is well-defined, in Lusss slates less so, while in Aberfoyle slates it appears as a small lip on the usual white mica peak.  It was found that the Royal Cottage samples lacked the double peak of Luss and Bute slates, matching instead the shape of the peak of Aberfoyle slates in the database.  This observation was substantiated by comparing selected  trace element concentrations of the Royal Cottage samples with those in the database.  It was therefore decided that the Royal Cottage slates were from the Aberfoyle group of quarries.

 

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