Besides, you can take the help of an electronic carat reader since gold is measured in carats. Gold in its purest form is a weak metal and is usually mixed with the other metals to make it stronger. Just put the piece on the tester and get its carats. Remember a 24 carat measurement is the purest form.
Then you can also go for the acid test since gold is known to be non-reactive to acids. Just pour a few drops of hydrochloric acid or nitric acid to check the degree of change in the piece which would determine the rate of mixture.