Funny,

The thing about parkerizing is actually interesting. From a thread on DecoStop i cleaned some very rusty Steel 15l. last year with a phosporic-acid solution. This can give a very thin parkerized protection inside that holds up better than raw steel. Cleans out the rust nicely as a black phosphate-solution. Some in my diveclub predicted I would die on first dive afterwards (apparently they don't know whats in Coca-Cola)

See:
The Deco Stop (Long thread)
Parkerizing - Wikipedia, the free encyclopedia