While the sword body is now complete, the swordsmith's work is far from over. Just prior to firing the sword a final time, he paints a thick, insulating mixture of clay and charcoal powder onto the blade's upper sides and dull back edge, leaving the sword's sharp front edge only lightly coated. This serves both to protect the blade and to give it its signature wavy design called the hamon, which later polishing will reveal. The swordsmith then places the katana back into the fire to be heated to just below 1,500 degrees F; any hotter and the sword might crack during the next step.