Early chemists only investigated on high-value materials to humans, such as gold and copper. gold was very valuable because of its properties such as color, luster and that it didn't tarnish. Copper was also valuable because it could be used to make pots, coins, tools, and jewelry. Untreated copper is brittle and weak. However, when copper is heated it can be rolled into sheets or stretched into long wires. Later experimenting with copper let to the creation of a strong hard material known as bronze, which is made when copper and tin are melted and mixed together.