Black siliceous pebbles suitable for assaying use as touchstones, 1995

Made:
1995
maker:
Unknown

Buy this image as a print 

Buy

License this image for commercial use at Science and Society Picture Library

License

Buy this image as a print 

Buy

License this image for commercial use at Science and Society Picture Library

License

Science Museum Group
© The Board of Trustees of the Science Museum

Science Museum Group
© The Board of Trustees of the Science Museum

Several samples of natural black pebbles from various locations, selected for their suitability for gold assaying purposes when used as touchstones: Two black pebbles from the beach at Staithes, Yorkshire August 1995.

Touchstones are fine-grained siliceous stones, on whose abrasive surface a gold sample undergoing checks for purity would be rubbed. A streak of gold would be left on the stone’s surface, which could be compared against gold of known quality, to establish the sample’s purity. Touchstones were the main means of assaying the quality of gold throughout history, but remain in use today.

Details

Category:
Metallurgy
Object Number:
2019-89
type:
pebbles
credit:
Gift of Dr W.A. Oddy