Glad to see conch-L picking up after the holiday slump!  I was
beginning to wonder if my E-mail was working!
 
Hi Hilary and all,
 
I have cleaned thousands of bivalves with bleach, and have not noted
any loss of shell pigment.  Like land snails, some bivalves, such as
Mytilidae, and some Veneridae, may have a dark, shiny periostracum,
while the underlying shell may be lighter in color and less glossy.
What kind(s) of bivalves are you referring to?  Are they beach
specimens or live-collected?  Of course, with bivalves there is no
problem removing the soft parts from inside the shell, so the only
reason for using bleach is to remove periostracum, or algae and other
contaminants, from the exterior.
 
Acid on shells?  :-(  Best avoided if at all possible.  The only
legitimate use for acid (and some would debate that) is as a last
resort measure to soften or loosen heavy lime deposits on a shell
exterior.  This is often a problem with shallow water, rock-dwelling
forms like Morum, Thais, Haliotis, etc., and the appearance of such
shells may sometimes be improved by the judicious application of
dilute acid to the exterior, followed by immediate brushing and
rinsing.  There is never any reason to allow acid to touch the
interior of a shell, and this should be carefully avoided.  An ugly,
encrusted Drupa morum with a bright purple aperture can be turned
into an ugly, encrusted shell with a dull greyish aperture by a dip
in acid.  Always keep in mind that the problem with using acid to
remove limey deposits is that the shell is made of the same calcium
salts as the encrustations.  If the acid will dissolve one, it will
dissolve the other.  Hence, acid is always a last resort measure, and
for most shells should never be used at all.  Personally, when I have
shells that are so encrusted they would require acid treatment, I
just toss them in the reject bin.
Having said all that, if you must use acid - where to get it?  Start
with the supermarket.  Vinegar (dilute acetic acid) is often as
strong an acid as you will need.  Use it full strength.  However, if
you are trying to remove thick, hardened lime deposits, vinegar won't
be very effective.  In that case, a stronger acid might be tried.
Hydrochloric acid can be purchased from building supply places under
the commercial name muriatic acid.  They use it for dissolving
concrete off tools, etc.  It is a dangerous chemical!  It can cause
severe skin burns, and will damage just about any surface except
glass and most plastics.  Full strength, it will completely dissolve
an average size shell in about 5 minutes, accompanied by a violent
"boiling" action, as the carbonate of the shell is changed to gaseous
carbon dioxide.  This can cause splashing of the acid.  Therefore,
such acid has to be diluted before use.  A 5% solution (5 parts acid
to 95 parts water) should normally be adequate.  A 5% solution of
hydrochloric acid is MUCH more acidic then full strength vinegar!  In
making dilutions of acids, the standard rule is - always add the acid
to the water, not the water to the acid.  WEAR EYE PROTECTION in case
of a splash, and rubber gloves.  It will also burn holes in clothing,
so an apron of some kind might be advisable as well.  The 5%
solution, once prepared, is much less potent, but eye protection is
still a good idea when using it on the shells.
 
Paul M.