The outer casing has a certain strength to protect the inner casing and increase the decorative effect. The outer casing is made of tin-plated steel, brass, alloy aluminum, stainless steel and plastic. China also has black iron, bamboo, bamboo, wood and enamel. For ease of use and aesthetics, the casing can be used in a variety of shapes and decorations. Decoration methods include printing, painting, spraying, plating, spraying, polishing, engraving, dyeing, etc.