Since I wanted to give the impression of a brass/copper metal, I started the weathering with a turquoise acrylic paint. It looks just like the color I have seen on tarnished copper.
I thinned the paint a bit with water to help get it all around whatever "joints" or transitions existed in the jar.
Once I knew I had paint where I wanted it, I thinned it enough to really run and brushed it on pretty liberally so it got on the bolts and in the crevices. I used paper towels to dab the excess off and tone it down.