Corrosion refers to the natural or forced destruction of metal. Different metals corrode in different ways. Iron, for instance, corrode by transforming into iron oxide or rust when exposed to oxygen, while zinc forms a layer of zinc oxide on its surface, which later hardens and turns into zinc carbonate when exposed to atmospheric carbon dioxide.

The chemical agent that prompts corrosion affects each metal differently, too, as elucidated through the above-mentioned examples. Oxygen remains the most influential of all corrosion-causing elements due to its abundance, but various compounds, particularly acids, are many times more potent.

Corrosion impacts not just a metal’s appearance, but also its longevity. Especially if the metal has an assigned structural function, identifying and eliminating factors that could trigger corrosion is necessary to prevent accidents.

Stages of Corrosion

There’s a vast range of factors that affect the rate and manner by which a metal corrodes. These include metal type, chemical agent, metal composition, temperature, pressure, and a plethora of environmental factors. It is therefore safe to say that each metal type undergoes unique stages of corrosion when exposed to the same chemical.

To make it easier for us to understand how metals corrode, let us categorize them based on their iron content, since iron is a key player in the corrosion of many of today’s extensively utilized metals. Let’s call those that contain iron “ferrous metals” and those that do not “non-ferrous metals”. Assuming the chemical agent is oxygen, here’s how these two types of metals react.

• Ferrous Metals

  – Oxygen is present in the atmosphere, so unless placed in a vacuum, ferrous metals are bound to corrode. When a ferrous metal corrodes, oxygen molecules latch onto iron molecules, forming iron oxide. This continues until all of the iron within the metal leaches out.

• Non-Ferrous Metals

  – Metals like copper, bronze, and brass corrode almost the same way as iron and steel, except the damage stays on the surface. When oxygen molecules combine with the molecules of non-ferrous metals like these, a layer of oxide forms. Over time, this oxide combines with carbon dioxide to form a carbonate, which later becomes the metal’s protective layer.

The Noble Metals

There’s a group of metals that neither tarnish nor rust when exposed to oxygen. They are called noble metals. Platinum, gold, silver, and palladium belong to this group. Even prominent non-ferrous metals like copper and titanium don’t make the cut, because they, too, corrode. Want to know if your gold jewelry is authentic? Try not polishing it for days. If it stays shiny, it means it’s authentic.

Metal Polishing Process

Thankfully, corrosion can be fixed, depending on the metal type and the severity of damage. This isn’t the case with ferrous metals in which corrosion has already cut deep. Like a rotten tooth, there’s a limit to how much of a piece of ferrous metal has been consumed by rust so it can be considered non-salvageable.

It’s a different story when you are dealing with non-ferrous metals. As explained, the damage left by corrosion on these metals are only skin-deep, because the patina acts as a shield against further damage. Such shield can preserve the metal inside for a long time. To give you an idea how long, the oldest metallic artifact discovered was a copper awl, which dates back to 5,100 B.C. It’s surface is heavily corroded but the inside is intact.

Of course, it’s difficult to remove patina and restore a metal’s luster, which is why you should polish a metal when it’s just starting to tarnish. Tarnishing is the first stage of corrosion and it’s just a thin layer that can easily be polished by scrubbing with a homemade or commercial metal polish. Besides, scraping away the patina might damage the metal underneath, especially if it’s the soft type, so don’t wait for the metal to patinate before you polish it.

Then again, if you really need to polish a severely corroded metal item but you don’t have the right tools and polishing agent, opt for professional metal polishing services. They use cutting edge-technology, including powerful substances to eradicate even thick layers of corrosion.

Whether it’s a jewelry item or a raw metal piece you bought from one of the bronze or brass suppliers in your area, if it’s made of a non-ferrous metal like copper, brass, or bronze, it can be polished back to its shimmering self. Here are some simple tips you can follow.

1. Wash the metal piece with soap and water very carefully to remove dust and grease. Excess dust may contain tiny pieces of stones that can scratch the surface of your metal piece when you start scrubbing.
2. Dry the metal piece properly until it’s totally stripped of moisture. Water may not go well with the metal polish. Buffing while the surface is still slightly wet may not yield the result you desire.
3. Choose between a homemade polish and a commercial one. It would be easy to just buy over-the-counter metal polish, but if you’re the exploratory type, you can make your own metal polish by mixing boiled water, baking soda, and salt.
4. Rub the surface of the metal item with the metal polish mixture and let it sit for a few minutes. Then buff it with a clean cloth until the shiny surface emerges. Do this repeatedly until all surfaces have been fully buffed.

If ever you are interested in making metal furniture yourself, consider using any of the 100 different copper alloys. They’re not just rust resistant, but they are also visually appealing. Some brasses even have a gold-like shade, which makes them so elegant-looking. Just remember to buy your supplies from one of the top bronze and brass suppliers in North America, such as Rotax Metals. They offer some of the highest quality copper alloy supplies in the country.

Copper is widely known for many things. Most of us know it as the first metal discovered and used by man, preceding even gold and silver, yet strangely not as popular in ancient documents since it’s been utilized mostly for utilitarian applications. Because of the many useful properties of copper, major industries, such as transportation, construction, and telecommunication rely heavily on its production. As such, copper is also known as a barometer for the global economy, because its production reflects the current and future state of those industries.

In North America, we know copper as the material that make up many of our prominent landmarks, and one of the main reasons they still stand to this day. Best examples include the Library of Parliament in Ottawa, Ontario and the Massachusetts State House, which both have a copper roof. We also know that The Statue of Liberty in New York Harbor is also made mostly of copper. But a lot of us didn’t know that most of the old copper structures like The Statue of Liberty haven’t always been green. They were actually shiny, metallic-looking at first. The newly laid copper roof of the Massachusetts State House shows us a glimpse of how those structures used to look like.

But why did their color change? Have they been painted so they won’t rust like most steel structures? While coating the surface of metal certainly helps prevent corrosion, copper is different from other metals because it has its own way to protect itself from corrosion. In fact, the green color that it develops overtime is made up of a layer of patina, which serves as it shield.

What Is Patina?

Patina refers to the result of any aging process that causes discoloration or fading of a material’s natural color. The transformation of copper from shiny, reddish brown to green is actually the most popular type of patina formation. Bronze and brass undergo the same process, but that’s just because their main component is copper.

This aging process is generally known as oxidation. When a material, organic or inorganic, is exposed to oxygen, the oxygen molecules combine with the molecules that make up that material and create a chemical reaction. The kind of chemical reaction depends on the type of material involved. For instance, diced potatoes or fruits turn brown when exposed to the air. Iron rust in a moist environment. The oxidation that these materials undergo is actually a process of degradation, since it eats away at the material layer by layer until it’s reduced to dust.

Copper, on the other hand, experiences oxidation rather distinctly. Chemicals in its environment that make contact with its surface also cause reaction, but instead of breaking down on a molecular level overtime, it creates a layer of protection that prevents those chemicals from further digging into its core.

It’s important to note that oxidation isn’t always caused by oxygen. A lot of other elements and substances can cause the same reaction on metals. Quite many chemicals, apart from those that are naturally present in the air, can oxidize copper, including ammonium chloride crystals, copper sulfate and ammonium sulfate. These chemicals are used to bring out that uniquely elegant, greenish color of copper.

How to Oxidize Copper

When oxidized, copper can change into a shade of green, but not instantly. It normally takes many years of constant exposure to natural elements before that elegant, jadish green shade appears. In fact, you will see it transform into different shades of brown before it turns green. Fortunately, the oxidation process can be expedited so you can achieve the shade that you desire for your copper items. Here’s one way to force oxidize copper.

Most harsh substances are capable of oxidizing copper, but you don’t need to buy special acids just for that. Basic products like vinegar and salt can have the same effect. All you need is enough amount of these products to submerge your copper item for a certain period. So let’s say your item is just a piece of copper jewelry that you’d like to give a rustic, green appeal.

The first step is to thoroughly clean the jewelry to get rid of all traces of oil and dirt. After rinsing away all the suds, sprinkle a little bit of baking soda and scrub the surface of the jewelry with steel wool. That should remove any excess contaminants or coating stuck on the surface and allows the copper layer to be exposed to the oxidizing agent. Then wash off the baking soda without touching the jewelry with your skin.

Depending on the size of the jewelry, mix three parts of vinegar and three parts of salt well until you can no longer see salt crystals. Put the item into the mixture and let it soak for at least 30 minutes. After it’s fully soaked, take it out of the container and place it on a clean paper towel. Don’t wipe it; let it dry on its own. You can sprinkle a little bit of salt on its surface to further speed up oxidation.

Knowing simple ways to oxidize copper lets you stretch out your creativity. It can even open doors of opportunity for you in the craft industry. Nevertheless, don’t forget that it’s also important to get your copper supplies from a reputable supplier. Otherwise, the metal you will work with might not react correctly with the chemicals you will use. Top suppliers in North America such as Rotax Metals offer the highest quality supplies on the market. You might want to put them on your list.

Sources:

https://www.dailymail.co.uk/news/article-2037582/The-copper-Statue-Liberty-appeared-New-York-1880s.html