Cleaning a big sheet of badly tarnished brass

[genec]

At an estate sale last year I found a big chunk of tarnished brass. I think I spent about $70 on it. It's 36" square by 1/4" thick. It's heavy---took two of us to get it safely down the steep basement stairs.
It's also badly tarnished, as you can see.
I'd love to know what kind of brass it is, 260? 464? 280? Nowhere seems to have 360 in this size, so I don't think that's what it is. Is there a way to tell?

No idea what I'll do with it, but when I do, I think it would be nice if it didn't look like it had graced the bottom of the parrot cage for a decade.
Anyone have a great shortcut to get this clean? I do have a Cyclo polisher which will help if I know what to use on it.

View attachment 247490
I know I can turn a profit taking it to the scrap yard, but I'd rather make something.

try a bottle of katsup

 

[Cadillac STS]

What does the other side look like? If the other side looks nice and clean maybe just flip it over so it looks better until you decide what to do with it? Because it is very possible one side is all that is needed to be clean based on the purpose.

 

[bfk]

Thanks everyone for the ideas. Maybe I'll have some time this weekend to experiment. I'll post the results when I have them.

Unfortunately the other side is just as bad, so no easy out there.

Does anyone have any ideas how to tell which type of brass it is?