weathering copper: stop me if you've heard this one.
I don't know if this has been done before, but I figured this out by accident while experimenting w/ some weathering for wood panels w/ some shoe polish. I accidentally got some on the copper hull of the ship I was working on, and when I tried to rub it off, well...It looked really good to me. So this time I did it on purpose for the hull of the Constitution that I am currently building. The pics below aren't the best. Lighting was a problem, but it shows pretty well the before and after. Makes the copper look like an old penny and highlights the plates and rivets really nicely. (bottom is untreated Testors copper) It's really shiny right now, but after I get some dull-coat on, that will tone it down.
Here's what I used.
I literally gave it a shoe shine. I applied the polish w/ a cut off brush so that the bristles are stiff. I did relatively small sections at a time being careful to get an even coat of polish (not too heavy) , let it sit for a minute, then used the shoe brush on it.