Parkerizing is a technique used to add a phosphate coating to steel to provide it with protection against wear and corrosion. This coating is typically composed of a zinc phosphate, though it can also use iron or manganese instead. It cannot be applied to nonferrous metals such as copper and aluminum, and even steel that has a high content of nickel can be unsuitable. The techniques is most commonly used on guns, and has been a popular alternative to bluing since the middle of the 20th century. Most parkerized metal takes on a matte gray finish, though some techniques can result in a darker black color.
The technique of parkerizing is based on iron phosphating processes that were first carried out in the late 19th century. Similar manganese phosphating was also experimented with in the early 20th century, which ledto the development of parkerizing around 1915. A new process with the same name was developed around 1938, which used zinc instead of manganese. Since zinc was easier to come by and less expensive than manganese, this became the more popular method at the time.