Toilets are commonly made of ceramic (porcelain), concrete, plastic, or wood. Major types include earthenware, stoneware and porcelain. It is a primary raw material for many ceramics such as earthenware, stoneware, and porcelain. Common examples are earthenware, porcelain, and brick. Designs were painted in cobalt blue on white porcelain. The Palace Museum holds 340,000 pieces of ceramics and porcelain. Most are made of porcelain or borosilicate glass. The art of porcelain and ceramics can be seen at the Noritake Garden. Less common materials that have been used include wood, glass, crystal, porcelain, and bone. Restorative materials include dental amalgam, composite resin, porcelain, and gold. Overhead conductors are usually air insulated and supported on porcelain, glass or polymer insulators. These gates are decorated with Chinese porcelain in floral patterns. Crowns are often made of gold, porcelain, or porcelain fused to metal. The "Erya" defined porcelain () as "fine, compact pottery ()". Jingdezhen is widely regarded as the producer of the best porcelain in China.