Definition: The Treaty of Kanagawa was an 1854 agreement between the United States of America and the government of Japan. The treaty, which was essentially imposed on the Japanese by threat of force, opened two Japanese ports for trade with American ships.
The first plates were made of sheet iron, but tin became the standard by about 1920. The State of Arizona made its tags from sheet copper in 1932-1934. Porcelain plates were also quite common in the early days of vehicle plates, and Delaware was the last state to make porcelain plates in 1942.
Most plastic plates are made from a material called polystyrene. According to Encyclopedia Britannica, polystyrene is a polymer of styrene, which is a compound of carbon and hydrogen. Polystyrene can be traced back to 1839 when apothecary Eduard Simon isolated an oily substance from storax, a type of natural resin.