Touchstone (assaying tool)

A touchstone is a small tablet of dark stone such as slate or lydite, used for assaying precious metal alloys.

It has a finely grained surface on which soft metals leave a visible trace.

[1] The touchstone was used during the Harappa period of the Indus Valley civilization ca.

[3] The touchstone allowed anyone to easily and quickly determine the purity of a metal sample.

Drawing a line with gold on a touchstone will leave a visible trace.