There are two main materials in a kitchen faucet. There will be a base material, which provides the structure of the faucet, and an external finish that protects the faucet from the outside and creates its overall appearance. The best internal material is brass, which is strong, durable, and resistant to corrosion.
The external finish will usually be a metal such as stainless steel or brushed nickel. White kitchen faucets usually have an enamel finish, similar to modern sinks and bathtubs.