Fill a spray bottle halfway with water. Pour ammonia into the bottle to fill it the rest of the way.
Spray the diluted ammonia onto the dirty ring around the tub. Allow it to sit for two to three minutes to cut grease and oil stains.
Wet a nylon mesh sponge with the ammonia spray. Sprinkle baking soda over the sponge.
Scrub the porcelain surface to remove the dirty ring. Rinse the sponge frequently to remove soil. Add more ammonia and baking soda and continue to scrub.
Remove particularly stubborn porcelain bathtub ring stains by sprinkling salt onto the sponge, along with the baking soda. Scrub the surface to remove the remaining stains.
Rinse the porcelain bathtub to remove the homemade cleansers and dirty ring stain.