scope:

A black protective coating can be applied tn ferrous metal parts by several processes in which different chemical solutions or compounds and application procedures are used, but all of these finishing systems, with the exception of MIGC-QSC, grade I, consist of four basic operations, i.e., cleaning, retreating, processing, and oiling. The MIGC-490, grade I coating is not oiled, since this is a preparatory coating for painting or similar coating. The purpose of the processing and oiling operation is :

(a) To provide the parts with a low-cost, non reflective, protective coating, which is firmly bonded to the underlying metal and which will afford maximum resistance obtainable by the coating system employed to abrasion by manual handling and operational wear.

(b) To protect the metal from ambient moisture, fumes, perspiration residues, and other deleterious agents, which might, by corrosive action, impair or destroy the usefulness of the item.

Obviously this protective coating will be ineffective if its continuity is broken by surface defects that are points of entry for corrosive substances. Such imperfections are unavoidable ,unless the metal surface is completely free of dust, grit, grease, oil, acid and alkaline residues, rust, and other contaminants when the protective coating is applied.