631-5.3.6.1 GENERAL. Rust converters are a broad class of commercial products intended for use on rusted steel to chemically convert the surface rust layer to a more tightly adherent oxide. The resulting surface is usually black or near-black in color. When a quality rust converter is properly applied, the resulting surface film can provide a limited amount of short-term corrosion protection, preventing further rusting until proper surface preparation and coating can be performed. Rust converters are usually based on phosphoric acid or tannic acid, and are generally not intended for use on non-ferrous metals. In particular, they shall not be used on aluminum alloys, where they can cause accelerated corrosion.
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