Rust is ferrous oxide, common(oxidation) red rust on ferrous metal (iron/steel); bluing is a process that causes the formation of ferrosic oxide (black finish) referred to as bluing. Bluing is a "traditional" finish. There are many ways to produce a blued finish and other "traditional" finishes that are accepted. All "old school" finishes, including parkerized, are a chemical process affecting the surface of the ferrous metal.
Duracoat ect.... are surface treatments ( call it paint for simplicity) that are bonded in some manner or by propriatary magic to the steel. There are benefits to each system of finishes regardless of appearance. Some, like Robar, are done to produce a more lubricious (sp?) finish and others to just coat/seal the steel.
There is only one goal; protect the steel from oxidation (rust). In my opinion the largest factor in refinishing a gun is your preference for appearance.
Duracoat ect.... are surface treatments ( call it paint for simplicity) that are bonded in some manner or by propriatary magic to the steel. There are benefits to each system of finishes regardless of appearance. Some, like Robar, are done to produce a more lubricious (sp?) finish and others to just coat/seal the steel.
There is only one goal; protect the steel from oxidation (rust). In my opinion the largest factor in refinishing a gun is your preference for appearance.