The cast iron has a rough surface, which can be better combined with enamel. The cast iron bathtub will be fired after spraying the bottom glaze. Each time the enamel is enamelled, it is fired at a high temperature of 850-870℃ to form a strong vitrified enamel surface. Impurities will not penetrate into the surface of the bathtub and can be cleaned by flushing with water.