I recently found some Astarte/Tridonta (mostly A. elliptica) shells which
are almost certainly subfossil dating from the last ice age, but in almost
perfect condition, complete with periostracum. I allowed the first one I
found (unfortunately the only A. borealis) to dry out, and the periostracum
flaked off immediately, as soon as the shell was dry. I have kept the
subsequent finds in the clay and brackish water in which I found them, and
would like to know the best way of preserving these, bearing in mind that
they are probably subfossil and I particularly want to preserve the
periostracum.

I have been advised by a leading expert in ice-age molluscs in the UK where
I live that the best preservation method is to use gum tragacanth as it is
water-soluble and can easily be removed at a later date. He has had great
success with this. But as I have a number of shells, I would also like to
know of any alternatives that I could try so that I am not relying on one
method.

I know this has been discussed before (particularly in April 2002 under the
subject of "oiling shells"), and from what I have read, parafin seems to be
the best bet for preserving periostracum, though I do not really want to
introduce any foreign substance if it is not completely necessary,
particularly in case they were to be subsequently used for research or as
museum exhibits. If I use parafin, would the shells need to be completely
dry first? I doubt if the periostracum would survive complete drying.

The shells have somehow been preserved buried in clay for thousands of
years, and possibly more recently in brackish water, and I am wondering if
there is some way of replicating this natural method of preservation for at
least a short period of time. Would keeping the shells immersed in saline
solution (in glass or plastic tubes so they could still be seen) preserve
the periostracum?

Sarah Longrigg

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