Porcelain enamel has a high-gloss finish and is easy to clean. The downside is that it can chip and crack easily, creating a "hole" in the finish that exposes the metal underneath and leaves it open to rusting. Such a chip or crack calls for immediate repair. Depending on how large the damaged area is, you may be able to repair your porcelain enamel sink yourself.
Sand the porcelain chip or crack; having a smooth surface to repair is key. Make sure no fine pieces of porcelain enamel are lingering inside or around the chip or crack.
Clean the area with soap and water, applied with a soft cloth, to remove dirt that could prevent the repair compound from adhering properly.
Mix the porcelain repair compound -- porcelain epoxy and an alkyd-based paint -- on a ceramic tile with a tongue depressor. This is the best method for making sure the compound doesn't get contaminated.
Apply the compound to the chip or crack with the razor blade. The blade allows you to use as little or as much compound as needed, and scrape off any excess compound very precisely.
Let the repair compound dry completely, according to the package directions. Remove any dried excess compound with a cotton swab dipped in nail-polish remover. Wipe the swab around the edges of the repair.