Natural rubber, before processing, exits the tree in the form of a white, milky latex. Therefore, the natural color of rubber is white. However, rubber is made black by adding various chemicals, such as carbon black, during the manufacturing process. Carbon black works as a reinforcing filler in rubber, which increases the durability and strength of the end product. The use of carbon black in rubber was originally proposed by Binney & Smith, the same company that invented Crayola Crayons. Nowadays, silica is also used as a filler material for rubber tires, which has similar reinforcing properties as carbon black but leaves the rubber white. However, silica-based additives have much worse abrasion wear properties than tires with carbon black.