When the Jōmon people discovered the chemical change that hardens clay when it is burned, they started making earthenware. All kinds of vessels can be made from clay. The earthenware can also be heated. The invention of earthenware made it possible to eat plants that normally cannot be eaten, thus further enriching the cuisine. In the late Jōmon period, people began making earthenware of various shapes and sizes to suit different needs. Adding to the traditional deep pots, they made vases, bowls, shallow pots, vessels with spouts, lipped vessels, and censer-shaped vessels, one after the other. Urns for cooking, storing, and serving food as well as for burials also came about.