Scrub loose rust off the gate using a wire brush. Detach as many rust flakes as possible.
Apply naval jelly liberally onto the remaining rust using a disposable paintbrush. Thoroughly coat the rusted portion of the gate with naval jelly. Wear safety glasses and durable rubber gloves when handling the naval jelly to prevent the chemicals in the product from burning you.
Wait 30 minutes for the naval jelly to fully dissolve the remaining rust on the gate.
Rinse the gate with water to thoroughly flush off the naval jelly. Do not leave any naval jelly on the gate.
Rub medium-grade sandpaper over the affected area to smooth the metal and eliminate any rust particles the naval jelly didn't dissolve.
Moisten clean, fine-grade steel wool with mineral spirits while wearing the rubber gloves. Scrub the pad across the metal to clean off grease, soil and anything that may disrupt primer and paint from adhering to the gate.
Rinse the gate thoroughly with clean water. Dry the exposed metal with a clean towel.
Spray a smooth coat of alkyd rust-inhibitive primer onto the exposed metal immediately after rust removal. Let the alkyd rust-inhibitive primer air-dry according to its instruction label.
Apply 2 separate finish coats of alkyd enamel paint onto the dry alkyd rust-inhibitive primer using a paintbrush. Let each coat of alkyd paint air-dry separately according to its instruction label.