Moisten a steel wool pad. Scrub the surface of the gas stovetop burner grates to wear away the rust. Rinse off the steel wool pad as the rust stains are lifted.
Rinse the burner grates with water to wash off the loosened rust. Add two or three drops of dishwashing detergent to a nylon mesh sponge. Scrub the exterior of the burner grates to clean the surface.
Run water over the burner grates to rinse off the detergent. Pat-dry the cast iron with paper towels to remove moisture.
Heat your oven to 450 degrees Fahrenheit.
Pour 2 tablespoons of cooking oil into a small bowl. Apply the cooking oil to the surface of the burner grates with an unused paintbrush.
Position the oiled burner grates on a baking sheet. Place the baking sheet in the oven and allow the burner grates to cure for 30 minutes.
Turn your oven off and let the burner grates cool completely inside the oven. Remove the grates from the oven and pat-dry to absorb any excess oil.