The shell is a festive holiday popcorn tin about 10 inches in diameter and 11 inches tall. This was lined with a layer of castable refractory insulation approximately 2″ thick. The foundry fired with charcoal with the cricuble in place and loaded with chunks of scrap aluminum. Even with the fire inside hot enough to melt aluminum (1200 to 1400 degrees F) the insulation is effective enough to keep the paint on the outside of the can intact. In fact, I can touch the outside of the foundry BRIEFLY with my bare hand without injury. Link.
Coffee Can Foundry