Touchstones were essential tools once used to determine the quality of precious metals. The metal or alloy in questions was rubbed against a small tablet of dark stone which has a finely grained surface, such as slate or basalt, and the stearks they made were compared with the set markings from an alloy o known high quality composition. The process was called probing. In the days when gold and silver were in use as currencies, touchtones were indispensable. Since gold and silver could very easily be alloyed with metals of much less quality, and rendered less valuable, the use of touchstones made it possible to test for such forgeries quickly and efficiently. The practice paved the way for gold and silver become the standard equivalents of value to government issued currency which started out as coins made of pre probed alloys.