Discuss PGroot's answer to: How can you identify gold from other metals?

The magnet test: if there's iron in it, a magnet will attract it.

The acid test: pure gold does not react with nitric acid.

The density test: pure gold has a density of 19 g/ml which is higher than most metals.  18K gold has a density of 15 to 17 g/ml.

The wear test: if it's just gold plated, the plating may flake off revealing a different color.