me too. I just carbonize the mess and scrape it off.I've put them in the oven on the Clean cycle and they come out looking new.
The only way I know of is to take to a ceramic place and have it glazed. Other then that just use it. Took about 6months of a heavy use to get mine were it needed to be. And I make a batch of bread about every 3-4daysDo you folks season your stones?