repair crack in porcelin tub?

have a hairline crack in porcelin tub. like something was dropped on it. starting to spread over the yrs. like spokes on a wheel kind of. maybe 12" out from point. dont think it leaks. need to fix crack then maybe repaint or reglaze or refinsh. tub not really discolerd. but want it to blend in.

Phillip Strand
December 2009