after checking around I found that Powder Coating is the LEAST desirable as it adds bulk to the parts. it is a baked on finish not unlike Enameled Cast Iron bathtubs. it can and will chip.
there is a liquid solution that actually changes the color of the metal below the surface. won't chip and harder to scratch. I've heard that coffee grounds are used to create an antique look.
dura-coat is another 'baked' finish that is chip resistant but will scratch.
I have opted for a ceramic application that is used on engine exhaust headers. like Top Fuel Dragsters, Funny Cars and Pro Stock. you will find it on NASCAR, Indy Car, Drag Boats and Air Craft. it is a tough product and highly scratch resistant, darn near scratch proof. it won't melt. the metal it is attached to melts/fails. they use it on the tops of pistons, turbocharger housings and gas turbine exhaust. it comes in many colors too.
look for Performance Coatings in your neighborhood and check them out. when my parts are finished Friday, I'll post pics and have a range report by Monday. also helps if the shop is run by Gun Owners so the $70 is being well spent. the Dark Slide of Sigma, the AF, put a spell on me. my 'copy' will be that special touch that makes it personal
Ron