Scott- If you go to your local pool store, you can purchase a liquid chlorine
that is far stronger than bleach, and does not cost much more. However, this
liquid loses strength over a period of days, unlike bleach. For some large
shells like Busycon contrarium, which are mostly white over 14", after
bleaching for a day, I'll leave them outside in the sun. After a week or so,
any barnacles or growths usually crumble off fairly easy. I obviously wouldn't
do this with shells that would fade their colors in the sun.    Scott