The best materials for storing and repairing shells are those that do not
harm the shell, even after many years have passed. Whatever you do should
also be reversible.

Rubber bands deteriorate badly within a few years, eventually turning into
strips of brittle material that are stuck to the shell. The transformation
can be delayed by placing the specimen in darkness, but eventually this
will happen.

Glues work because they react with the surface of the shell, so it's a good
idea not to use them for keeping valves together. (Even the "temporary"
glue on yellow sticky-tab paper will glue permanently onto your book pages
within about 5 years, as I have discovered by experience.)

Wax is a special case. It is not very reactive, but it is also very
difficult to remove from surfaces later on, so anything you do with wax (or
silicone, for that matter) must be considered as irreversible.

I have seen string used to hold unionids together, with no harm to the
shell after about 70 years. This string has a peculiar golden color, and I
do not know its composition or brand name.

In many collections, gravity is used to keep valves together, with one
valve resting on the other, both with the interior of the shell oriented
downward. I don't recommend this in earthquake country, or in collections
where people handle the shells often. But if you write the specimen number
on both valves, they can always be reunited.

The collector can simply store each pair of valves in its own box, bag,
tray, or compartment. Ideally, paper containers should be of archival
quality (not acidic); we have discussed suppliers of chipboard trays and
rag paper in previous threads. Wood is not recommended in the very long
term, especially acidic wood like oak. Metal works well, at least as a
cabinet material. Plastics are of diverse compositions, and some of them
deteriorate rapidly, which is not good when you are using bags to keep the
shells separate. Other plastics are of archival quality. I have had some
plastic bags split in the dark in only ten years. As to cotton, the Conch-L
archives have a thread on that too, with mixed reports. Some cotton seems
to be low enough in acid to work well for a hundred years, but some people
have had bad experiences with the stuff. Catalogs of archival-quality
materials are distributed to librarians and museum curators. I haven't
checked, but they are probably accessible through the Web now.

I was amused to hear about the recycling of fast-food containers for use in
the shell collection. This is a great way for a beginner or someone with
limited resources to get started in shell collecting. As a poor grad
student, I used to save plastic vegetable trays from the grocery store, and
would cut the bottoms off waxed-paper milk and juice containers for use as
small square trays. After thorough washing, they worked very well for a few
years, until I replaced them with chipboard trays.

Anyone who collects fossils knows that some rocks are acidic. Fresh
sandstone and shale commonly contains pyrite, which oxidizes in the
atmosphere to iron oxide (rust) and sulfuric acid. After a few years,
opening a drawer full of such specimens yields a sour odor, and your fresh,
bluish-gray rocks have turned yellowish-brown! Where the shells have been
replaced by iron sulfide (pyrite or marcasite), the fossils themselves are
the problem. When freshly collected, these fossils are colored a beautiful
brass-yellow. After a few decades, they convert to a pile of greenish-gray
dust in a badly discolored paper tray, with a more or less shell-shaped
hole eaten through the underlying paper label. The inevitable can be staved
off by various chemical means, but generally not forever. On the whole, it
is best to store such specimens separate from any specimen that might be
damaged by acid vapors. But most fossils in limestone can be stored along
with modern shells without fear of harming them, so far as I know.

This has been an interesting thread. I'd like to hear from museum curators,
shell dealers, and others who deal with decades-old collections about their
preferences for very long-term storage of paired valves. For instance: Does
string work for several decades for specimens that do not have a protective
periostracum?

Andrew K. Rindsberg
Geological Survey of Alabama
Tuscaloosa, Alabama, USA