Rust
Rust, and I don't mean the programming language du jour, is an unending fascination of mine, representing as it does a wonderfully complex interaction between ferrous materials and oxygen itself. On the face of it, rust would seem to indicate irreversible decay and despoliation of otherwise solid and reliable material. On the other, it is simply the natural combinatorial action of a reaction between a metal and a reactive element, resulting in the formation of an oxide of that metal. The beauty of it however, is that the resultant oxide can be reduced and reversed chemically, as anyone who has studied basic chemistry at school will know. The oxidation of iron of course can lead to violent reactions as well as the gradual oxidation of itself into rust, however, given sufficient heat and fuel. Iron Oxide III or red iron oxide [rust without the water-based component, if you like] for instance, provides a very good source of oxygen to fuel a thermite reaction in a number of reactive me...