Under the pot! You can use them for fighting, too - in Skypeia, there was this guy that had a giant bird with a Flame Dial in its mouth, so it breathed fire, and he had a Heat Dial in his lance so he could burn and stab you at the same time. Other people had Burn Bazookas, Flame Bazookas, kept them under a glove in the palm of their hand... It's really useful!