The black oxide coatings covered by this specification are military unique. Black oxide coatings are used on munition cases and gun barrels. These coatings are particularly suited for moving parts that cannot tolerate the dimensional build up of a more corrosion resistant finish. They are not recommended on parts going into long term storage. Sometimes, long term storage is required and a protective preservative fluid is recommended or a desiccated package is utilized. The coatings present a pleasing black appearance frequently employed for decorative purposes or decrease in light reflection. A supplementary water displacing preservative coating such as MIL-PRF-16173, grade 3 or comparable material which will provide equal or superior corrosion protection may be specified.

CAUTION: High strength steel (40 HRC or greater hardness) may be subjected to "caustic embrittlement" that could lead to spontaneous cracking if under internal or applied stress during the blackening treatment.