Wednesday, 11 February 2015

The Geological Detective - II


The Triton Stone Library

Having established that none of the samples in the Triton Stone Library could offer a good match to the stone used in the subject building, the next step was to obtain samples of stones that might be suitable to undertake the necessary repairs.

E-mails were sent off and phone calls made and I soon discovered that the quarry, which has been considered to be the primary source of this stone, has now been mothballed and that I would need to search elsewhere for a good match.

Stone matching in practice...

Time is of the essence, when planning and scheduling an extensive programme of works in the building restoration industry, and the first samples of stone were sent by a tried and tested contractor, who has a good working knowledge of the region.

The samples of Oat Hill stone from the recommended alternative marketed by various companies finally arrived, but a quick inspection with a hand lens revealed a medium grained, shelly oolite - with voids - which bears little resemblance to the subject stone.

The Art of Stone Matching is based on deep geological knowledge, and an understanding of chemistry - but it also relies on intuition, which microscopic analysis just can't reproduce. 

This particular compact, fine grained, moderately well sorted oolitic limestone is left with a very distinctive iron stain when subjected to a standard hydrochloric acid test.