Why And How Does Copper Oxidize?

The process of oxidization is not one that is altogether unfamiliar to us - iron is subjected to rust (a flaky layer of reddish brown metal), aluminium to corrosion (white flakes of metal), and even food can go brown if it's left out of the fridge for too long. In the same way, copper is also subjected to the oxidization process - when exposed to oxygen for an extended period of time it begins to turn green. Copper's original colour is often described as being pink or peachy with a distinct metallic shine. When it oxidizes, the metal reacts with oxygen, which forms a copper oxide on the item's surface. It is this oxide that possesses the distinct green colour. A coating then forms over the top, known as a copper patina, which actually forms a protective layer around the metal and prevents it from oxidizing further. But why does the oxidization turn the metal a green-ish colour? In short, during the oxidization process the elements of the copper lose electrons (these are usually identified as being hydrogen ones) as they react with external elements, such as oxygen. Many people actually like the green oxidization that copper develops after exposure to oxygen over time - it can make the metal appear highly attractive and gives the item a distinct old-fashioned touch. As people are impatient, however, they have begun to look for other ways to get this oxidization to occur and have managed to simulate a similar effect using chemicals. By mixing together a formula of copper nitrate, ammonium chloride, calcium chloride and water, you are able to cause your copper items to develop the green oxidization you so desire in minutes rather than years. Once you have mixed the solution up, all you will need to do is submerge the copper items and leave them to dry. Another way to achieve oxidization chemically it to take a solution of liver of sulphur, heat it and apply it to the surface of the copper item. You will need to use a spray bottle to do this and apply it to the metal whilst heating it up with a torch. Once you have finished spraying the surface, you can rub it down using a wet scourer. Then, reheat the surface with the torch and apply a weak ferric nitrate to it. Instead of the green oxidization discussed above, however, this process will create a more brown or red colour. Copper oxidization (or patinas) can be formed in a number of colours, including: green, brown, red and even blue. By experimenting with different chemicals, you can create different effects - just remember not to mix chemicals unless you know what you're doing and avoid using bleach.