Perhaps you own brass or bronze jewelry that has a green patina over time. Or you may have noticed that these metals can stain your skin green. But why does this happen and why is patina necessary?
Brass and bronze contain large amounts of copper. When copper oxidizes when exposed to oxygen, a greenish patina forms that protects the metal
from further corrosion. The higher the copper content of the metal, the greater the chance of a green patina.
WHY BRASS, BRONZE AND COPPER TURN GREEN
The greening process of copper takes different amounts of time depending on the conditions. In very dry climates, copper can take up to 20 years to turn green. The transition from normal color to green occurs in stages. First the copper dulls, then turns brown, dark brown and eventually green. If ammonia is used, this process can take as little as a few hours. When you see a green layer on these metals, commonly called a patina, it means that a chemical reaction has taken place. The copper has reacted with oxygen, water, and carbon dioxide in the atmosphere.
Copper oxide is something like "rust", although rust is the word used to define iron oxide. This means that if there is no iron, there is no rust. But both are types of oxides.
When you see a green layer on these metals, usually called patina, it means that a chemical reaction has occurred. The copper has reacted with oxygen, water, and carbon dioxide in the atmosphere.
Brass is an alloy that is usually made up of 67% copper and 33% zinc. Bronze is made up of 88% copper and 12% tin.
Both of these metals have a very high copper content, so they develop the same patina when oxidized.
USES OF COPPER OXIDE
Copper oxide is a popular material for finishing various decorative items such as brass door handles, copper roofing and others. But aside from the aesthetic aspect, there are practical reasons why patina finishes can be useful.
First, it provides protection for the metal.
Copper oxide is an interesting substance that adheres well to the base metal and is durable. The thickness of the copper oxide layer determines the degree of protection against corrosion. Unlike iron oxide, which flakes off, exposing a new layer of metal that is susceptible to rust, copper oxide prevents further oxidation.
An example is the Statue of Liberty, erected in 1886. Even after more than 130 years of exposure to natural factors, the copper oxide layer is only 0.005 inches thick. That's about the thickness of two sheets of paper.
WHEN COPPER OXIDE IS NOT SUITABLE
There are several situations where copper oxide may not be desirable.
For example, if you wear copper jewelry, you probably don't want your skin to get a greenish tint. Also, if you prefer the bright look of copper instead of a dull greenish color, a patina finish may not be appropriate.
Copper oxide is also not a conductor of electricity. Given that copper is widely used in wires and electrical connections, copper oxide buildup can cause problems.
WAYS TO GET THE GREEN COLOR OF COPPER
Copper or other metals with high copper content will turn green on their own over time when exposed to air and water, but what if you want to speed up the process?
Here's one way to quickly patina small pieces of copper:
First, thoroughly clean the metal of grease with a degreaser. Oils can prevent oxidation and patina from forming. Then fill a quarter of an airtight glass jar with ammonia.
Hang the copper on a string over the ammonia inside the jar. Close the jar. Within a few hours, the ammonia vapors will cause a thin patina to form. If you want a thicker coating, leave the metal in the jar for a longer period of time.
HOW TO REMOVE COPPER OXIDE
It is actually very easy to remove, and there are a number of ways to do so.
For example, if you are trying to remove green oxide from coins, you can simply soak them overnight in acid. Also, simple brushing and scrubbing will help get rid of the patina. There are also several cleaners (usually containing acid) designed specifically for cleaning copper-containing metals. You can also simply use an abrasive disk if the copper has a matte surface.
To clean electrical connections, it is common to use a wire brush and a strong acidic copper cleaner, which will take care of the problem quickly.
Copper oxide is actually very dangerous to cookware. It is toxic and you need to avoid ingesting it in food. Copper cookware is quite popular and needs to be cared for regularly. Since it is usually polished, you will need special cleaning products.
If the problem is a slight tarnishing rather than green oxide, using household acids such as lemon juice and a sponge will usually remove the problem areas without too much trouble. It is a good idea to polish the copper with an inhibitor afterward, as acids can etch the metal and make it prone to oxidation in the future.
HOW TO PREVENT THE FORMATION OF COPPER OXIDE
The easiest way to prevent copper, brass and bronze from turning green is to simply clean them regularly. Under average conditions, it may take a few weeks for the patina to form.
Nevertheless, caring for the item is a hassle. So, if you don't want to remember to clean copper, there are several alternatives.
Clear coated options are most popular for items such as findings and jewelry. There are hundreds of products designed to protect against tarnishing or patina formation to keep copper looking shiny.
Clear nail polish is also good for protecting copper. This method is more popular for things like jewelry.
A very old-fashioned way to preserve copper is to polish it with beeswax, it protects the metal very well from moisture and oxygen.
