Touchstone (assaying tool)
A touchstone is a small tablet of dark stone such as
lydite, used for assaying precious metal alloys. It has a finely grained surface on which soft metals leave a visible trace.[1]
History
The touchstone was used during the
Harappa period of the Indus Valley civilization ca. 2600–1900 BC for testing the purity of soft metals.[2] It was also used in Ancient Greece.[3]
The touchstone allowed anyone to easily and quickly determine the purity of a metal sample. This, in turn, led to the widespread adoption of gold as a standard of exchange. Although mixing gold with less expensive materials was common in coinage, using a touchstone one could easily determine the quantity of gold in the coin, and thereby calculate its intrinsic worth.
Operation
Drawing a line with gold on a touchstone will leave a visible trace. Because different alloys of gold have different colors (see
karat
gold is not affected but 14 karat gold will show chemical activity.
See also
References
- ^ "Touchstone". Oxford English Dictionary. Retrieved 10 March 2013.
- ISBN 978-0313-384318.
- ^ Bisht, R. S. (1982). "Excavations at Banawali: 1974–77". In Possehl, Gregory L. (ed.). Harappan Civilization: A Contemporary Perspective. New Delhi: Oxford and IBH Publishing Co. pp. 113–124.