Chris,
 
Personally, I like most shells cleaned up of all extraneous stuff.  I have
soaked some encrusted abalone in almost full strenght Clorox for over a week
with no lost of color (of course that is a pretty tough shell).  The
encrusted material must still be brushed off with a wire brush and mostly,
picked off with a dental pick.  I was recently given (for Christmas) a
really nice Murex saulii.  It was very nice looking but had never been
cleaned.  Soaking and cleaning this shell was a wonderful experiance as all
of the deep browns and light  pink highlights all of a sudden were right
there.  Before cleaning the shell was neat looking and had a great shape but
mostly muddy coloring.  After cleaning the shell was stunning.
 
The only shells I have that I have left uncleaned are: Conus dorreensis
(removing the periostracum takes away the pattern), Tricotrophis cancellata
(it has a hairy perio with little hooks), Glossus humanus (I think it looks
more heart-like with the perio left intact), Perna viridis (it wouldn't be
the green mussel without the perio) and Mitra idae (nice looking black
perio).  There are others, like some of the cymatium, but that is what comes
to mind right now.  I do know people who have shells with little or no
cleaning as they like them in a "natutal" state.  Well, for most shells, a
dried and crusty periostracum is a far cry from the natural state.  If you
really want the natural state you have to do like Dan Yoshimoto who has a
couple of aquariums with a variety of living seashells.  A really neat
display.  Oh, I also have a couple of small pecten that I have never cleaned
because they are just too delicate.  I don't want to trade a clean broken
shell for an uncleaned, unbroken shell.
 
So, like most everything in this hobby or whatever, you have a wide range of
choices and lots of folks on every side of whatever choice you make.
 
Tom Eichhorst in New Mexico, USA
 
Chris Brown wrote:
 
> Question:
>
> One of the recent posts indicated a way to remove calcareous deposits
> was to soak the shell in full strength bleach.  I was under the
> impression that this was not a good thing to do - at least for anything
> other than a short period of time.  I've got a number of specimens I
> would like to clean up, but am afraid of damaging the colors.  Is there
> a school of thought that advocates preserving the shell in the condition
> in which it was collected - or is the general preference to clean them
> up as much as possible - or is it simply a matter of personal taste?
>
> Just curious,
>
> Chris