Copyright 2009 Eastern Plating Company Website Design by Graphical Media Services What Is Black Oxide? Black oxide is a conversion coating formed by a chemical reaction produced when parts are immersed in the alkaline aqueous salt solution operated at approximately 285 degrees F. The reaction between the iron of the ferrous alloy and the hot oxide bath produces a magnitite (Fe3 O4) on the actual surface of the part. It is possible to oxidize non-ferrous metals under suitable conditions to form black oxides. It is possible to apply black oxide at room temperature, however it is not possible to achieve all of the benefits available from the "hot" oxide process. The cold black oxide process routinely shows color variation from part to part and the black material frequently rubs off in your hands. The cold process does not meet military or automotive specifications. Therefore the remainder of this article addresses the "hot" black oxide process. The five basic steps for the black oxide conversion coating are clean; rinse; black oxide; rinse; supplementary coating (after-finish). If rust or scale is present on the part, additional steps such as acid pickling or alkaline de-scaling may have to be added before oxiding. Neutralizing and/or further rinsing may be necessary on assemblies and parts with blind holes to eliminate "flowering" or bleed-out. Black oxide cannot be produced over plated parts (zinc, nickel, chromium, cadmium, phosphate). This plating must be stripped prior to the black oxide process. Black Oxide USEFUL AND INFORMATIVE LINKS www.astm.org - Search and purchase ASTM Specifications www.sae.org - Search and purchase AMS Specifications. www.finishing.com - Finishing information and forums assist.daps.dla.mil/quicksearch - Search and download Military Specifications. www.anodizing.org - find valuable information about the metal finishing process of aluminum anodizing