Why do iron articles lose their shine gradually?

Iron articles lose their shine gradually when exposed to the atmosphere. Iron is a reactive metal. Thus when exposed to atmosphere it reacts with atmospheric oxygen and moisture to form an iron oxide which is commonly called rust. Rust is a brownish coloured layer which gets developed over the surface of iron over a period of time. The reaction for the given change is as follow:

2Fe(s) + 3H₂O(aq) → Fe₂O₃(s) + 3H₂↑(g)