Refinish a bathtub using a reglazing kit, available at home improvement stores and online. For professional-looking results, remove any oils and soap residue from the bathtub before beginning.
Begin the process by removing any caulk between the tub and tile surfaces. Use a caulk removal tool or a utility knife to cut the caulk away from the edges of the tub and surround. Use needle-nosed pliers to pull the caulking material away once it loosens. If silicon caulk is on the tub, use a caulk digesting product to remove any final traces.
Clean the tub by scrubbing it with an oxalic acid scouring powder and a green scrubbing pad. Rinse the tub well, and scour it again, paying particular attention to the area around the drain. Failure to clean this area is the most common cause of unsatisfactory results with the reglazing kit. Dry the tub with paper towels.
If the porcelain contains any defects, fill them with a polyester filler similar to what auto body repair shops use. Mix the product according to the package directions, and press the filler into the defects. Sand the area after the repairs to smooth the surface. Use an orbital sander to sand the entire tub before applying the new finish.
Clean the dust from the tub, and apply acetone to dry the surface. Follow the manufacturer's directions for applying the new glaze.