After-rust is a form of

rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH ...

which sometimes develops on a non-ferrous metal surface when that surface has been finished, deburred, or cleaned with a

carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...

brush or

steel wool Steel wool, also known as iron wool, wire wool or wire sponge, is a bundle of very fine and flexible sharp-edged steel filaments. It was described as a new product in 1896.''Iron Age'', Vol. LVII, p.871, cited by ''Journal of the Iron and Steel ...

. It is caused by microscopic deposits of the steel which become embedded in the metal surface and which over time begin to oxidize. This oxidation causes the surface to become dull and may impart a brown color to it. After-rust can be avoided by cleaning such surfaces only with non-ferrous brushes/ wools including rustless bronze, aluminum, and stainless steel wool and nonferrous wools such as those made of brass.

References

Corrosion {{corrosion-stub