Touchstone bought in the bazaar, Istanbul. It is typical of the pieces of Blackstone brought in from the Turkish countryside, which were usually cut into slices by the goldsmith before being sold. Previous identifier: 1987-1

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 perhaps the main means of assaying the quality of gold throughout history, but remain in use today.