(710) NHRC-5 NHOU Rustoration Rust Converter & Prep (5g)New Hampshire Oil Based Undercoating Rustoration Rust Converter & Prep (5 Gallon Pail) Part Number: (710) NHRC5 NHOU Rust converter is a rust inhibiting coating that converts rusted metal in 20 minutes into a rust retarding, paintable surface. When applied to rusted surfaces, iron oxide (rust) is chemically changed to iron phosphate, an inert, hard substance that turns the metal black. This increases the paint adhesion and durability of the coating.