Why is rust red?

When a piece of metal goes through a process of oxidation, it is said to have rust or rust formation.  Most rust that people see on iron has a reddish or orange color, and so when people think of rust, they usually think of it as red in color.  From the term “oxidation,” one can assume that oxygen is involved in the process of rust formation.  And, true enough, oxygen is the main chemical that sort of initiates the formation of rust on metals.  Being dissolved in air, oxygen is able to come in contact with iron, for example.  And when this happens, iron will react in a way that rust will form on many parts of its surface.

Chemically, upon contact with oxygen and iron, iron oxides will form, and these usually come as a reddish color.  This is the simple reason that people always associate rust with a reddish color.  Some people think it’s more brownish or orange, but the color of iron oxide pretty much falls into the red and orange sides of the color wheel.  During oxidation, what actually happens is that the iron oxides formed will remain in the water, but as it evaporates, some of the particles remain on the iron’s surface. These particles are what people see as a red coating on the metal’s surface. There are also parts on the surface that resemble flakes and dust which are also part of the rust formation.

But without the presence of moisture or oxygen on metals, rust will not form.  There are also other metals that are quite resistant to oxidation and so they do not rust easily.  But in the strictest sense, rust could actually form in a different color. This happens when another type of metal is exposed to moisture. But since the most commonly used metal is iron, most rust that people see is reddish in color.

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