Since this is a favorite subject of mine, I'll mention that home parkerizing is pretty expensive unless you're doing alot of guns. The three big things you'll need are
1) Sandblasting cabinet set up with 80-grit Aluminum Oxide
2) Parkerizing chemicals (phosphoric acid, Zinc Phosphate / Manganese Phosphate, cleaning solution) - Brownells is very good.
3) Stainless-steel tank & burner setup (180 degrees F) (and optional steel tank for cleaing solution).
The two most important factors are:
A) Getting a good deep cut down to fresh steel with the sandblasting media
B) Getting the steel absolutely clean and absolutely oil-free after sandblasting
If you do those two steps, then the actual parkerizing step is very easy and nearly foolproof (assuming you've got your chemicals at the proper solution and temperature).
I collect & build Soviet AK's from kits, and this is my parkerizing setup. Note the stainless tank in foreground, and the steel tank on the stove in the background:
Here's what a part looks like when it comes out of the cleaning solution after parkerzing...
The hard part of refinishing is to try to get the correct finished color. This is where the 'art' comes in. It's pretty easy to gets shades of black... It's very difficult to reproduce that elusive 'green' that you sometimes see on original 1911A1's and some 1903A3's. I think the reason is because part of that color is due to oxidation over many years and thusly is difficult to simulate...
Here's an example of a typical grey/black that I've done in my garage. It's a great match for mid-century Eastern-Bloc weapons & more the modern US military parkerizing you'd find on an M16A1 for instance:
Blueing is quite different from parkerizing, but requires the same attention during the preparation phase. The biggest difference is that blued rifles are generally best on smooth metal (which requires glass beads instead of Al-Ox when sandblasted). The chemicals are considerably more caustic as well, which puts it into a somewhat risky catagory for home-builders. The parkerizing solution is pretty safe in comparison, but you still need to use common sense tools like eye and skin protection, and very importantly a full-face organic breather.
Just thought I'd share since I don't often get to contribute on this forum due to my newbie-ness with Japanese stuff.