I can't keep out of trouble. Asking advice again: [View all]

A neighbor had a yard sale today and of course I went. Bought a wonderful Circa 1850 brass bail handle pot. OK, it was filled with pine cones and they went into the trash but:

After dumping the cones, I saw...(wonderful)...that the bottom 2 inches were incredibly tarnished. Actually, I think she might have had a plant in the pot. Anyway, I spent the day trying to clean the tarnish off. It is more than tarnish inside, it is some kind of residue. The outside looks fine(I use "Brass Boy brass polish), the inside needs help.

I googled how to remove this crud in as many ways as I could. So many rec's to use baking soda and vinegar(maybe salt too). I tried the polish today, used 000 steel wool then wet & dry sandpaper. It still looks awful.
Tomorrow is another day. Any suggestions before I start this job again? I want to hang this on a crane in my fireplace but not like it looks now.

As always, help is appreciated.