Clay pcarpet pad off of cast iron heating grate

I recently purchased a hundred year old house that is in pretty terrible disrepair. I took out all of the carpeting, and in one room I found horrible clay carpet padding stuck to the oak floor. After spending three weeks hand scraping it (and trying various chemicals such as goof-off) I gave up and hired a company to scrape, sand, and refinish the floors.

The floors are beautiful! However, the cast iron grate attached to the floor still has the horrible green clay pad attached to it. I have no idea how to clean it off. I don't want to use anything abrasive as I don't want to ruin the new finish on the floor. On the other hand, there is so much detail to the grate that I'm not sure just using a pumice stone on it is going to take off all of the yuck.

Any suggestions?

 

is there a way to remove the grate? if so a sand blasting media may work