Parkerizing

Parkerizing, also known as phosphating, is a metal finishing process that creates a corrosion-resistant coating on ferrous metals. The coating is a conversion layer formed by immersing the metal in a phosphating bath, typically containing zinc or manganese phosphates. The resulting coating is porous and matte, providing an excellent base for oil, wax, or paint and helping to reduce glare.

History and usage: Parkerizing originated in the early 20th century with the Parker Rust-Proof Company, and the name has become generic for zinc phosphate coatings used on steel. It was widely adopted by military forces, especially for small arms finishes during World War II and after, due to its durability, ease of application, and ability to accept subsequent coatings.

Process overview: The sequence generally begins with cleaning and degreasing the metal surface, followed by immersion in a phosphating bath. The chemical reaction forms a crystalline phosphate layer on the steel. After rinsing, the part is usually oiled, waxed, or painted. The finish is typically a dull gray to olive color, with a surface that can retain lubricants and resist small amounts of corrosion.

Variants and characteristics: Zinc phosphate finishes are common for general corrosion resistance and as a paint base. Manganese phosphate coatings offer greater wear resistance but less corrosion protection and tend to appear darker. Parkerizing is appreciated for its rugged appearance and ability to hold lubricants, but it is not as hard or wear-resistant as modern hard coatings.

Applications: Used on firearms components, tools, fasteners, and machinery parts, where a durable, oil-retentive finish and good paint adhesion are desirable.