For those that haven't seen my post about me acquiring an antique forge recently, the picture of it is below. I wanted your advice on how I could make a firepot about softball sized with extra flat space (I don't know the specific name of it, like a table) around it for holding coal. Since my forge is a rivet forge it did not come with a firepot and with the tuyere about half an inch above the bottom of the pan. My idea was putting dirt into the bottom of the pan so it would fill in that half an inch under the tuyere. Then I'd make the firepot out of sheet metal. The pan is 18" diameter. Thoughts on this idea or if you have another idea?

Could just use clay and shape it to what ya want/ need.

I guess I should have mentioned, I don't really want to use clay. But if there are no other options I will have to do that.

That's just what I would use with what I've seen. I'm sure there are others with great ideas on it. 

More then one way to do things. 

Clay worked great for me, but you could always put a brake rotor in the middle as your firepot and fill the rest with sand. 

I have a similar forge for travel /demo work and it originally had a refractory type lining about 1 1/2 inch thick.  I took it out to lighten the load, and since that forge just heats up 1-2 times a month ill deal with the slow decay of metal.  originally the mortar was just placed in it level except for a small bowl depression in the middle with the bottom being the air inlet.   With a rivet forge that's all that was expected, just to heat rivet sized metal to forging temp.  to get a hotter fire for big pieces or forge welding you'll need to bank the sides up with more coal, but with that there's the extra consumption of coal.  probably getting off topic.... don't reinvent the wheel, just line it with a refractor mortar, or kitty litter homemade mix, there's liner recipes of all types just do a search on "homemade refractory mortar"