By restricting our discussion of plastic coatings, we omit many of the most widely used and most important protective coatings for metal. These include the many paints and oleoresinous materials using red lead, zinc chromate, iron oxides, metallic aluminum, lead, zinc and copper, as well as the whole group of asphaltic and bituminous compounds so largely employed as protective coatings for pipelines and other large-scale metal projects. These work-horses of the industry may lack the glamour of the newer synthetic plastic materials and they may be replaced by them in time, but it would give a distorted picture of the coating field if their importance were not mentioned.
There are many definitions of "corrosion.” For the purpose of this discussion I shall define it as the resultant of the combined effects of the environment upon the metal. These systems vary tremendously in nature, and the requirements for corrosion-resistant coatings vary...
