There is slight corrosion on ... the surface of the metal. Using paint or grease creates a barrier which physically stops oxygen/water from reaching the metal. An example is shown below.

Gold and other very unreactive metals do not oxidise in air at all. Corrosion close corrosionThe destruction of a metal by oxidation or chemical action, eg rusting. happens when a metal continues ...

The object of his experiment was to testthe rate of corrosion of metals in fresh water ... has provided a lodgement for moisture. Take for example a bar of iron in a field, and a similar piece ...