Hard anodizing, also known as hard coating or Type III anodizing, is a process used to create a hard wearing, 

corrosion resistant coating on a variety of metals. Anodizing can be broken down into two broad sub-categories: 

decorative and hard anodizing. The main differences between the two is how thick and durable the coating is, and

 the exact process used to create it.

Anodizing is an electrochemical process that converts the metal surface into a decorative, durable, corrosion-

resistant, anodic oxide finish.Anodizing a metal part involves putting it into a liquid that is electrically conductive, 

typically an acid solution, called an electrolyte. Circuits have a positive electrode (cathode) where electrons

enter and a negative one (anode) where they leave; in anodizing, the metal part becomes the negative electrode.

When an electric current is passed through the solution, the action of the electrons leaving the circuit through 

the metal part causes a tough, corrosion resistant coating of oxidization to build up. The coating can either be 

left as it is after this treatment or further enhanced with decorative dyes and other performance-improving 

additives.

The process of manufacturing hard anodized parts differs from decorative coatings in several ways. It uses electric 
currents that are generally higher and electrolyte solutions that are slightly weaker. The temperature of the 
electrolyte solution is also lower allowing for less distortion of precision parts and better adhesion of the coating. 
Generally speaking, the anodizing process is also considered to be relatively environmentally friendly and the 
byproducts are recyclable.