Assaying with Touchstones
- AThe resulting metallic streak left on the stone surface was then compared against reference marks made by needles of known alloy purity.
- BMerchants resolved this uncertainty by drawing the edge of a coin across a dark, fine-grained slate known as a touchstone.
- CBy applying dilute acid to these streaks, an assayer could dissolve base metals and determine the exact gold content with remarkable accuracy.
- DIn the ancient marketplace, verifying the purity of precious metal coins was essential for preventing fraud.