A chemical conversion coating that turns a ferrous part black with almost no dimensional change.
A chemical conversion coating that reacts with a steel or stainless part's surface to produce a black magnetite layer, adding color and mild protection without building up dimension.
Parts are immersed in a hot alkaline oxidizing salt bath, which converts the outermost layer of the steel into black iron oxide (magnetite) rather than depositing a separate coating on top. Because the reaction consumes surface material instead of adding to it, the dimensional change is on the order of a few microns — negligible for most tolerances. Parts are typically sealed with an oil or wax afterward, which is where most of the finish's actual corrosion resistance comes from.
Common on fasteners, tooling components, shafts, and brackets that need a low-cost black finish without adding thickness — especially where the part still has to fit a mating tolerance after finishing.
Steel, stainless steel. Full applicable-materials list, color range, and which finishes can combine are confirmed per order — see the Materials & Finishes page →
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