What are they made out of? Aluminum?
The kitchen in my house looks like an old french street scene. Broken plaster over brick walls, tile roof outcrops, etc. But just two weeks ago I added a downspout from the roof outcrop. I made it out of copper and aged it with a variety of household chemicals.
If you want a bit of green, mix 1 part bleach, 1 part water and lots of salt. Also mix up some miracle grow. Pour the bleach/salt mixture over it, then immediately pour a small amount of miracle grow over. Let sit for a few hours, repeat several times. Don't worry about getting it too green, after it dries, you can brush off as much or as little as you want with a wet brush. To make it permanent, seal it with clear laquer. This will also deepen the color of the green.
I found that Kaboom, makes most metals brown to black, depending on exposure. To make it permanent, seal it with clear laquer.
For rust on steel, or corrosion on aluminum. A strong mixture of bleach, water and salt will work well over a period of days.
Uric acid ages metal very well and it's free. Set the badge in the back yard and pee on it for a couple of weeks. To make it permanent, seal it with clear laquer. (The badge not your tallywacker)
You would think that swimming pool oxidizer would work really well, but don't do it. From experience, it outgases so fast that in less than 5 seconds you will have a mustard cloud around you. I think my throat still hurts.
Whatever you do, try the patina mix on the back first.
-=theron