Hi, (Other) JK.
I didn't suggest that because usually the Parkerizing has picked up so much oil that it is hard to get a good bluing over it. If the oil can be removed with some combination of solvent (alcohol?) and boiling, that will work, but remember that the reason for Parkerizing is that it retains oil, so it does not give it up easily.
Hi, Gary,
Obviously, sand blasting will work, but it also obliterates markings, so it depends a bit on what is wanted. If only a shooter is involved, a few markings more or less won't matter, but if one wants, say, to try to restore a Parkerized Model 1911 pistol to something like the original blue, heavy polishing or sand blasting will do a lot of damage. In the process of "sporterizing" (I plead guilty) I reblued a fair number of Model 1903A3's by polishing off the Parkerizing and sometimes there was almost nothing left of the model number markings or barrel markings when I got the last of the Parkerizing off.
Jim