Hi again, Robbin --
Can't find this one. Don't clean it. There were many "century of progress" medals minted for the Chicago exposition, but this one must be somewhat rare. I've looked in my reference material and don't see it.
The one in my picture is different. It sold for $100 US dollars to a collector. Yours might be worth about that, but I have no sure-fire way of knowing. There are several other patterns. They are called "so called dollars" but they really are commemorative medals.
I encourage you to look further if you can. If you find it, please let us know.