Determine if gold is real by looking for a hallmark purity stamp, checking for magnetic attraction or performing a nitric acid test. Real gold is not attracted to a magnet and does not react when tested with nitric acid. Additionally, real gold is heavy and will sink when dropped into a jug of water, so if a piece of jewelry floats, it's unlikely that it's made of real gold.
Most jewelry made of genuine gold is marked with a gold jewelry hallmark that describes its purity. Look for the purity stamp of 10K, 14K or 24K on the clasp of a gold bracelet or necklace or on the inner surface of a ring. However, the absence of a certifiable stamp does not definitively prove that a piece of jewelry is not real gold, especially with vintage or older jewelry.
Some specific markings signify that the gold is fake, such as G.F., which means gold filled; G.E.P., which means gold electroplate; and R.G.P., which stands for rolled gold plate. Costume jewelry, including the brands Esposita, Avon and Monet, often bears the designer's distinctive mark. To check for gold plating, lightly scratch the jewelry surface, and apply a drop of nitric acid. A green reaction indicates gold plating or a base metal. A milk-colored reaction denotes gold plate over silver.