Years ago I read someone used Porc-A-Fix, which is used to fix chips in enameled cast iron sinks, tubs, shower bases Never tried it myself though. It's sold on Amazon
PORC-A-FIX INFORMATION PAGE
Porc-A-Fix offers a simple way to repair unsightly chips, scratches, small cracks and other imperfections in porcelain tubs, sinks, toilets, tile, and porcelain
www.fixture-fix.com
