Take off the tub fixtures using your wrench. Tape plastic tarps around the floor and surrounding walls with masking tape.
Put on the rubber gloves and respirator.
Brush hydrofluoric acid over the porcelain of the tub with your paintbrush, putting it on in a thick layer. Let it sit for about 15 minutes. Rinse it off. Let the tub dry for 24 hours. The surface should be dull.
Fill the airless paint sprayer with porcelain primer. Coat the tub in a thin, smooth coat of primer.
Let the primer dry for four hours. Spray on a second coat of primer. Let it set for 12 hours.
Refill the paint sprayer with porcelain enamel. Spray over the tub in a thin, smooth coat.
Let the enamel dry completely for four to six hours. Apply a second layer coat of enamel in the same manner as the first. Let it dry. Apply a third layer. Continue for four to six layers until you achieve the desired look.
Allow the final coat to set for 48 hours. Reinstall the tub fixtures.