There are two common methods to accurately identify the fineness of gold jewelry.
(1) touchstone method: select a black touchstone with fine texture, draw traces on the touchstone with standard gold test pieces (for gold medals) with different gold contents, then scrape the gold jewelry sample to be identified on the same touchstone, add concentrated nitric acid to remove impurities, find out the traces left on the touchstone, compare with the drawn gold test pieces, find out the same chromaticity as the jewelry sample, and compare the standard degree of the gold sample, that is, the accurate gold content of the gold jewelry sample to be tested.
(2) Chemical method: also known as reagent spot test. Gold alone is insoluble in nitric acid, sulfuric acid and hydrochloric acid, while silver, copper and other components can react with nitric acid and be dissolved. Take samples of gold ornaments. If nitric acid is placed in a certain part, it will not change color if it is made of gold, and it will turn black if it is made of silver. In the case of copper products, bivalent copper salts will be generated and green bubbles will be emitted. Gold ornaments with gold content above 95% have little surface change when tested with nitric acid.