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Only Iron and steel rust. Other metals corrode. Rusting is an oxidation process. What we normally call rust is a flaky red-brown solid which is largely hydrated iron.

 The primary corrosion product of iron is Fe(OH)2 (or more likely FeO.nH2O), but the action of oxygen and water can yield other products having different colors: 

  • Fe2O3.H2O (hydrous ferrous oxide, sometimes written as Fe(OH)3) is the principal component of red-brown rust. It can form a mineral called hematite.
  • Fe3O4.H2O ("hydrated magnetite" or ferrous ferrite, Fe2O3.FeO) is most often green but can be deep blue in the presence of organic complexants as shown here.
  • Fe3O4 ("magnetite") is black
(Red-brown flaky rust- Black magnetite- Blue/green unstable rust)

Image of Iron Corrosion Products1             Image of Iron Corrosion Products2              Image of Iron Corrosion Products3

How did we make these experiments-

For the first experiment we put a 5 cm finishing nail brushed with steel wool in a test tube containing 8 mL of tap water. The picture was taken three days later.

The second experiment was carried out with an acidic solution containing 12% acetic acid. You can produce a similar reaction with vinegar which typically contains 3% acetic acid in water. However, you will have to be more patient than we were.

In the third experiment  a pellet of sodium hydroxide (caustic 'Drano') was dropped in the test tube of the second experiment. The test tube was capped to prevent air to react with the solution. After three hours the rust precipitates had more or less settled out has you can see in this picture.
 
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