kosketinsä
Kosketinsä is a Finnish term that translates to "touchstone" in English. It refers to a type of hard, fine-grained rock, typically a dark color like black or dark gray, that is used to test the purity of precious metals, especially gold and silver. The process of using a kosketinsä involves rubbing the metal against the stone to create a streak. The color of this streak is then compared to streaks made by known standards of pure gold or silver, or alloys of known fineness.
The effectiveness of a kosketinsä relies on its fine texture, which allows for a clear and distinct