Do you find yourself using the words corrosion, rust, and oxidization interchangeably? Especially when talking about metal that has experienced some wear and tear, or exposure to the elements? There are significant distinctions between these terms for changes or degradation in metal, and it can be helpful to understand the differences when choosing which metals are right for different projects.

Corrosion

A simple definition of corrosion is the breaking down of metal due to a reaction with its environment. The environmental factors that often contribute to corrosion include salt, temperature fluctuations, water or moisture, chemicals, or pollutants in the air. Corrosion is usually damaging to the metal.

How to tell if your metal is corroding?

Different metal types will show corrosion in different ways; here are some signs to watch for:

Aluminum and lead will develop pits or develop a white or gray chalky or powdery film.

With silver, you’ll notice blackening or tarnishing. Brass and copper show corrosion by developing a blue-green powdery finish.

Rust

Like the definition for corrosion above, rust is also the breakdown of metal. However, rust is specific to iron and steel. For rusting to occur, iron or steel, oxygen, and moisture interact to develop the trademark orange or brown spots. Unless the rust is very light and can be thoroughly wiped off, rust is always damaging to the metal.

How to tell if your metal is rusting?

To tell whether the area in question is impacted by rust, as opposed to dirt, paint, or fungus,  you can add a few drops of vinegar. If the area fizzes then the area has rusted. Further, if the rusted areas cannot be wiped off, and if it’s possible to flake or chip material from the area, it’s likely that the metal has significant structural damage. 

Oxidation

Oxidation, sometimes referred to as oxidization, is a chemical reaction that occurs when metal comes in contact with air. To put a scientific spin on it: when metal is exposed to air (or some chemicals like chlorine) the metal atoms lose electrons while the oxygen atoms gain them.

At its core, metal oxidation is an electrochemical transfer of electrons. When a metal is exposed to oxygen (or other oxidizing agents like chlorine or fluorine), the metal atoms lose electrons, while the oxygen atoms gain them. This reaction forms a metal oxide. Oxidation can either be damaging or protective. Rust is a kind of oxidation, and, as discussed above, is always damaging. When other metals oxidize they can form a protective layer.

How can you tell if your metal is oxidizing?

If aluminum is oxidizing, you’ll notice a dull white appearance. Brass or copper that has oxidized show a turquoise or green finish. Metals that can benefit from the oxidation process include stainless steel, aluminum, and titanium. These metals, as they react with oxygen, develop a thin, protective layer that helps block moisture and air from affecting the metal’s inner layers.