Sand the entire surface of the sink for 10 minutes using a small sanding buffer and a medium-grain sanding ring. Use small, circular motions as you sand. This will eliminate any areas of chipping or roughness.
Repeat this process to sand the surface of the sink using a fine-grain sanding ring. This will make the surface of the sink smooth and even.
Vacuum the sink and surrounding areas using a shop vacuum with a brush attachment. This will get rid of any dust and debris caused by the sanding. Wipe off the sink thoroughly using a damp washcloth.
Fill the bottom of a paint tray with porcelain paint, then coat the end of a 2-inch round paintbrush in the paint.
Apply the porcelain paint in a thin, even layer, then allow the paint to dry for eight hours.
Apply two more layers of porcelain paint onto the sink in the same manner as before, allowing the paint to dry for eight hours in between each layer.