Did you know you can take the finish off of metal with oven cleaner? I've done it before on bicycle parts ---- removed the anodization off of old parts and made them shiny silver again.
Well, in the battle of me versus the sink, the sink was winning: I couldn't get this thing to not leak. The metal drain ring is mostly plastic and it broke as I was tightening everything to eliminate a leak.
I looked in the box of parts from the old sink that was pulled out and the old sink ring was there and its metal. And it used to be brassy.
I liked the idea of metal, but the brass wouldn't do. So, I tried the oven cleaner trick.The trick is to soak it for 15 minutes or so, then scrub with steel wool, then repeat as necessary.
Here it is about 3/4 of the way done. There are still some small spots in the photo but I was able to get them out. I installed the ring, but it's still undecided if I've officially won the fight.
edit: here is the sink drain ring thing installed: