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Touchstone (assaying tool): Wikis

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This article incorporates information from this version of the equivalent article on the Japanese Wikipedia.

A touchstone is a small tablet of dark stone such as fieldstone, slate, or lydite, used for assaying precious metal alloys. It has a finely grained surface on which soft metals leave a visible trace.

History

Usage

Drawing a line with the gold on the touchstone will leave a visible trace. The trace will react differently to specific concentrations of nitric acid, thereby identifying the quality of the gold. Thus 18 Carat (purity) gold is not affected but 14 Carat gold will show chemical activity.

See also

  • Litmus, a test for pH levels

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