I polished up a door knocker for my former boss. Since it was exposed to the weather, it needed a protective coat. I used a laquer made for protecting metal. I don't remember what it was, but I found it in the local HW store, and it was name brand stuff. Krylon, I think, but I can't be certain.
Ayway, polish the part to perfection. Warm it slightly. I used my wife's hair dryer, but a short set in an oven would work, too. You want it warm, not hot. If you wouldn't hold it in your hand, it's far too hot. Warmth helps the laquer flow better to even out the coat. If it's too hot, the slovent's will flash off before it gets a chance to an even level.
Clean throughly. I used alcohol, applied liberally from a squirt bottle. Any fingerprints or dust will be trapped forever, so this part is crucial. Allow to dry (the warmth helps here, too).
Spray on (or brush on if that's what you have) the laquer. Thin coats. I say agan, THIN coats. As in, the first shouldn't even cover it completely. Wait 30 seconds, and spray/brush again. Keep doing this until you have total coverage. Avoid overbrushing. If spray, try not to get it on too thick. A second coat later is always possible, but runs are a real pain to remove.
Cover it. It's more important that it be kept dust and bug free than it dries quickly. Resist the urge to check on it. After about double or tripple the normal drying time, you can remove the cover and let it dry completely. Don't even try to pick it up until it has dried for 4-6 hours. Again, any fingerprints will be there forever.
The aforementiond knocker is still in place, and still looks good after almost 5 years, exposed to the elements.
