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I dont think it will explode. Porcelean fires to 2200 degrees F. And if there were any air pockets it would have exploded in the kiln. Maximum wrought iron forging temp is 2500, so you may see some reaction, but i dont think explosion is the risk. (Lots of ceramic firing experience, zero forge experience).
Does the charcoal stay suspended or does it settle to the bottom? If you made a pitcher of this ahead of time for a party would it remain black or seperate?
Nicely done! Any concerns about generating too much force on the front of the base plate that might strip out the two screws fastening it to the saw? Even just a couple of posts out towards the front would offer support.