Mar-Hyde® One Step Rust Converter Primer Sealer chemically reacts to convert rust into a hard, black primer sealer. Apply One-Step® on rusted surfaces and rust is permanently converted and ready for primer and topcoat. One-Step Rust Converter Primer Sealer is water-based latex containing rust modifiers, which is designed for application directly over tightly bonded rust on iron or steel. It's also proven effective on new degreased or mild steel where flash-rusting has occurred. Shortly after application, the rusted surface will change from white to purple to a stable black coating.