Rust remover being applied to rusty hinge. Phosphoric acid solution creates a chemical reaction when brushed on to rusty steel. It converts the rust into a water-soluble compound that can be scrubbed away. This chemical acts quickly and effectively, but it is very toxic. The active chemical, phosphoric acid, will cause chemical burns if it spills onto skin. Protective clothing, gloves and eye and face protection should be worn. It can also be used to clean brass, copper, bronze and chrome.