DIN 50938:2016-10

This standard specifies requirements and test methods for black oxide coatings produced on ferrous metal components by a chemical reaction during an immersion process. Room-temperature blackening by means of acidic solutions containing heavy metals, and other methods of producing black oxide coatings are not covered by this standard.
Black oxide coating provides iron and steel (for example, cast iron, unalloyed and low-alloy steel) components with uniform black coatings to give the material a particular appearance while substantially retaining their dimensional accuracy.
This standard does not apply to mechanical fasteners; agreements shall be made for threads on objects. This standard does not cover semi-finished products.
This standard has been prepared by Working Committee NA 062-01-76 AA "Chemische und elektrochemische Überzüge" ("Chemical and electrochemical coatings") at DIN Standards Committee Materials Testing (NMP).