
Image from: Weapon Universe
Bronze is a very common metal which is used industrially and to make art. The Sumerians first discovered bronze in 3500BC. That led into the less common Bonze Age. Bronze was used to make light, sharp swords and chariots. The Summarians mixed copper with arsenic to make items. Arsenic is brittle and was not effective in warfare.

Image from: CoinTalk
Bronze is not a natural element. In fact, in modern times, it is often a mixture of copper and tin. (No, they did not melt the tin man.) This combination of metals is called an alloy. When bronze is exposed to air, it will oxidize and leave a green, red, or brown tint to your bronze depending on the alloy. For some people this is desirable. However, if you start to see green power-like spots, this is undesirable and is known as bronze disease.