Carole,

I have have kept a number of thin walled Viviparidae and Pyganodon in
ziplock bags without any other treatment. They have held up well for the
past 10 years. A few which I did not put in ziplocks (an oversight)
cracked within a few months.

The ziplock bag, while permeable to moisture, isolates the specimen from
rapid changes in relative humidity and seem to protect specimens
reasonable well without "contaminating them with various chemical.

On the other hand, if the specimen is going to be part of a display or one
that will be handled by people, then some of the preservation techniques
mentioned would be worth a try.

I also offer the following which appeared in Chapter 2 of The Mollusks:
Aguide to their collection, study, and preservation

Animal and vegetable-based oils will become rancid with time and should be
avoided. Silicon oil is a relatively inert substance. Its stability, lack
of odor, and safety profile have made it a substance that people are
comfortable using. The silicon oil is cut with naphtha or mineral spirits
1 part to 2-4 parts. Shells are dipped into this mixture and then placed
on a flat surface. The solvent evaporates leaving behind a thin coating of
silicon. If diluted appropriately the amount of silicon oil remaining
should not leave the shell feeling greasy or tacky. Too much oil makes the
shell slippery and a “dust
magnet”. Mineral oils can be used in a similar fashion.

A number of collectors have used a solvent called WD-40® to brighten the
surface of a shell or to preserve the periostracum. WD-40 is a petroleum
distillate. Some collectors dilute it 1 part to 3-4 parts naphtha or
mineral spirits and then dip their
shells into this solution. Others use the WD-40 full strength. We do not
recommend WD-40 for one preservational aspect - it is a proprietary and
secret formula. Such mixtures are of unknown composition and can be
changed at any time. Thus, you are
never certain what you are putting on your shells. If you are going to
apply a coating to your shells, you do not want to apply it full strength.
This full strength coating will often make the shell tacky and slippery.
Many collectors dilute the oily substance with naphtha or mineral spirits.
Diluting the oil one part to three or four parts of solvent is often
sufficient. When the solvent evaporates, it leaves behind a thin coating
of the oil. Also, the thinned oil is able to penetrate into the shell
deeper than the full strength oil would. When using solvent, make sure
there is adequate ventilation and no sources of open flames. While naphtha
and mineral spirits are relatively low toxicity, they can act as
respiratory irritants. They are also flammable, thus no sources
of flames or sparking should be present.

Clench (1931) described a process of mixing paraffin with xylene. Place
120 g (4 ounces) of paraffin in 300 ml (10 ounces) of xylene. Warm this in
a water bath to dissolve the paraffin in the xylene. Shells are dipped
into the solution and then placed
on a flat surface to dry. The xylene will evaporate leaving behind a thin
coating of paraffin. Remember that xylene is flammable so avoid open
flames. Xylene is also a respiratory irritant, so this method should only
be performed in a fume hood or a well ventilated area such as outdoors.

You should also keep in mind that many collectors and most museum workers
apply no surface coating to shells. Generally, if you keep the temperature
and humidity level of your storage area within a range of 16-21ºC
(60-70ºF) and 50-55% relative
humidity, there should be no concern with the periostracum peeling (See
Chapter 5, Archival and Curatorial Methods). Also, there is nothing wrong
with a slightly faded, pristine shell as opposed to one that is shiny but
chemically adulterated.

Clench, W. J. 1931. A preventive for the scaling of the periostracum.
Nautilus 45: 30-31.


Regards,
Charlie
.................................................
Charlie Sturm

Treasurer
American Malacological Society

Research Associate - Section of Mollusks
Carnegie Museum of Natural History
Pittsburgh, PA, USA

Associate Professor - Family Medicine
Fellow-American Academy of Family Practice
Fellow-Academy of Wilderness Medicine

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