Parkerizing at home is done by a lot of folks. You can remove the old finish with phosphoric acid, naval jelly, or Birchwood Casey rust and blue remover, or by pickling in muriatic acid. Degas the parts after using an acid. You can also simply bead blast the parts, which is part of the pre-park prepping of the gun - it will remove all the blue. Whaen bead blasting though you'll want to mask off all of the mating surfaces, like frame rails, lug and cam ways, slide ways, bolt cam surfaces, etc...
Check out this site, they have a forum that will answer a lot of your questions
Parkerizing at home is a snap! I have the gun bead blasted to remove the finish, clean in acetone and use Brownells Amerelene parkerizing solution. You mix up the proper amount in distilled water, heat to 185 degrees and drop in the parts. It only takes five minutes in the solution. Then fish them out, rinse in tap water and blow dry, then spray with the Amerelens neutralizing solution, and re assemlbe.
If my wife is home, I do this in the garage on a Coleman stove, if she is not, use the kitchen stove (Idon't tell her)
Always use stainless steel pans to do this. I use a commercial food tray, like they use in a buffet.
The difections that come with the solution are simple to follow.
Brownells also sells zinc phosphate and manganese phosphate solutions, true mil-spec finishes, which don't etch to the degree that Amerlene does. Just as simple to use, though maybe a bit more temp control is required.
Biggest thing I found was the cleaning process of the parts. I I posted my mess up last year but the web album is gone with the pics. My problem was that I didn't get the excess oil off enough. It looked GREAT right out of the tank but when it finally dried there were big area's along the slide that the park didn't take to.
So make sure it extremely clean before you drop it in the park solution.
Also known as hydrogen-embrittlement relief. Acids will produce hydrogen gas that penetrates the crystal structure of the base metal. The hydrogen will embrittle the base metal unless you bake at low temps for a certain amount of time forcing the gas out of the metal.
www.techplate.com has a little section on hydrogen-embrittlement relief and instructions on how to degas.