After the surfaces are smoothed, the bowls and tanks are sprayed with glaze of various kinds to get different colors. This glaze is designed to shrink and contract at the same rate as the greenware while undergoing firing. After being sprayed with glaze, the toilet bowls, tanks, and lids are placed in stacks on a conveyor belt or "car" that slowly goes through a large kiln to be fired. The belt slowly moves the glaze-covered greenware into a tunnel kiln, which has different temperature zones inside it starting at about at the front, increasing towards the middle to over degrees, and exiting at about . During the firing in the kiln, the greenware and glaze are vitrified as one solid finished unit. Transiting the kiln takes glaze-covered greenware around 23–40 hours.