>One other thing. 3% hydrogen peroxide will generally loosen up or dissolve
>organic material that remains stubbornly in the spire. While calcium
>carbonate is impervious to hydrogen peroxide, remember that some shells
>aren't 100% calcium carbonate.


I have tried H2O2 on shells, as an alternative to perchlorite bleach, and
found that while it works far better on organics, it will also attack shell
organics ie the conchiolin matrix and pigments. I wound up with unnaturally
pale Astraea heliotropium and Calliostoma pellucidum. They will also be
rendered more brittle.

Andrew G