Normally an intermediate process is carried out before painting, called sandblasting: a mechanical process by which the most superficial part of a material is eroded by abrasion due to a jet of sand and air.
The so-called “sand” consists of a mixture of mineral and/or metallic abrasive grits with certain grain sizes and characteristics.

Painting, on the other hand, involves the creation of a protective film, a film, on the surface of the part.
This may be an organic coating, consisting of synthetic resins, or an inorganic coating, consisting of zinc powders and other binding elements, or overlapping layers of both.