Best way to remove dirt from an OLD horse-shoe?

I'm making a Christmas present for my trainer. I found a super old horseshoe buried in dirt a few months back and am making a pretty ornament out of it (planning to). The dirt on it is very hard and stuck to it, i tried scrubbing and it's not coming off... are there any chemical agents that can aid in the removal of old hard dirt? (i.e windex, scrubbing bubbles, etc)