This coating is a chemical black oxide coating of iron and iron alloy metals (wrought iron, low alloy steel and stainless steel). The coating is applied for parts used under mildly corrosive conditions as it provides limited corrosion resistance. Standard has defined 4 types of solutions. The most common of these are Class1 for Steels and Class 4 for Stainless steels. Class 2 and Class 3 types require high Occupational Safety conditions as they are made at high temperatures.
Smut Test, Oxalic Acid Spot Test, Corrosion Test (Class 4)
MIL-DTL-13924 (These standards are international, they are the main ones and they can also be customer standards.)