A testing solution, often provided in a set, is utilized to determine the purity of gold. It involves applying a small amount of acid to a scratch made on a touchstone with the item being tested. The reaction observed indicates the karat value of the gold present. For example, a solution formulated to test 14 karat gold will dissolve items with a lower karat value, leaving higher karat gold unaffected.
This method offers a relatively quick and inexpensive way to assess the authenticity of gold items, playing a significant role in jewelry valuation and precious metal trading. Historically, this technique has been employed by jewelers, pawn brokers, and gold buyers to verify the quality of pieces and prevent fraud, ensuring fair transactions based on accurate assessments of precious metal content.