Tuesday, 19 March 2013

100,000 Scottish thin sections completed! by Rachel Whitty

Since early 2012, a group of volunteers have been working flat out in Murchison House, Edinburgh to photograph the British Geological Survey’s rock thin section collection.

From the mid-1800s, thin sections have been created from rock samples taken from all over the UK. Today the collection includes about 100,000 sections from Scotland, 11,000 from Northern England and 80,000 in the England and Wales collection. BGS has been aiming to photograph these thin sections, to make them available to the wider public.


 S24582  Diopside in marble


Last week, the last thin sections from the Scottish Sliced Rock (S) Collection were photographed! All of the 100,000 thin section samples from around Scotland have now been photographed (two photographs of each) and will soon be available for public access on Britrocks, the rock sample database.

The process of photography of all these thin sections is mainly carried out by volunteers. Each thin section is individually cleaned, a necessary step since some thin sections have collected over 150 years of dust! Once cleaned, the sections are organised by collection number and the process of photography begins.


 
 S97329  Gneissose semi pelite + magnetite. 1km NNE of Meall na Bracldlach. SCOTLAND. Dalwhinnie (63E)


In order to ‘capture’ each thin section, two photos are taken; one using plain polarised light (PPL) and one in crossed polarised light (XPL). Officially, the reason for this is that different mineral properties are shown under different light settings, and this enables more close analysis of the samples. Unofficially, very plain-looking samples in PPL usually look a lot prettier in XPL. The surprise of improved appearance keeps the volunteers guessing, and can be helpful after several hours of photography.

A digital SLR camera with a 1:1 macro lens is permanently set up to complete the photography process. A custom-built frame places the camera in line with a stage for the thin section, analyser for light changes and LED lamp for illumination.



 S34093  'Original entry: Dyke'. Allt Laire. SCOTLAND. Glen Roy (63)
  
Once each thin section has been photographed, the Collection number and corresponding photo numbers must be matched for the database so that geological information about each rock thin section can be matched to the correct images.

All of the thin sections from the S Collection have been processed in this way, and the huge size of the collection which has now been finished is a definite accomplishment. However, no rest for the wicked, and the volunteers have now started on the Scottish & Northern England (N) Collection, which although smaller, still contains 11,000 sections.

Rachel Whitty, BGS Volunteer



NB: For more info on the thin sections and their image capture see Isla's Blog Post. To search more images go to our Geoscenic website, or to search through collections search our Rock Collections Database

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