Gold, recycling and lab safety

Metals change in different ways over time. Iron turns red-brown and flaky when it rusts. Silver slowly turns dark, and copper turns dull and later greenish. Gold is different. Gold does not react with most acids or with air and water, so it stays bright for a very long time. That is why the golden mask of Tutankhamun is still shining after more than three thousand years. The ancient Egyptians loved gold partly for this reason, and also because it is soft enough to shape. We say that gold is a stable metal: it does not easily change into something else. The metals that do change are not bad. They simply react more easily with air, water and acids, and a protective paint or coating can slow this down.