I've checked out some ideas online and some folks are doing some pretty creative things - check them out here and here and here. Clearly I could do something to buff up mine.
First step: Pop out the button. This was essential to my plan of doing two colors because I live to complexify any project! The popping thing wasn't as easy as it sounds! I tried prying out the button with no luck, but soaking the knob in hot water did the trick. Think it expanded the metal just enough to release the plastic button. ( I told you these were some high-quality hardware)! This one ( a spare test- subject) has some chips from my attempts to dislodge it prior to heating it.
Next I scrubbed them to remove any grime.
Then some spray primer - I like Kilz best. Word of caution - I thought perching the knobs in skewers stuck into florist foam was a good idea. Not so much - the foam shed little bits of grit that stuck on the knobs - maybe because it was an old piece? I had better luck perching the knobs on an old cookie rack - no sticking!
Then the buttons got a spray coat of Rust-Oleum Hammered Silver and the knob bases Rust-Oleum Hammered Black. These hammered paints cover minor scratches and can be painted over rust. The finish looks almost like a combination of some light glossy and slightly darker matte colors. I like that it's not really shiny and has a slight texture to it.
Then I sprayed on a coat of clear matte finish, although I don't know that it was really necessary.
Some of the buttons snapped back in easily, some did not, so they got glued in.
This project wasn't difficult, but I'm not going to lie, it was pretty tedious what with all those steps! But I love my new knobs and how they've dragged my cabinets into the current decade.