Many thanks to those of you who replied to my query about preserving
periostracum. The replies were very helpful.

As I had 3 pairs plus 4 single shells all with periostracum, I experimented
on the single shells.

I cannot get hold of ethanol as it requires a licence in this country (UK).
The best solution I can find is to use strong vodka or gin, but I have had
great difficulty in finding one that is 50%+, which I have been advised is
necessary for permanent preservation.

I therefore immersed one shell in 37.5% vodka. I also painted one shell
with paraffin, another with Gum tragacanth (1g in 100 ml of water with a
drop of formalin added to prevent mould), and left one untreated.

The periostracum on all the shells, apart from the one immersed in vodka,
started to crack as soon as they were dry. (Possibly the gum tragacanth was
too weak, but I'm afraid that using a stronger mixture might just delay
cracking rather than prevent it)

I am therefore favouring the vodka treatment, but will have to hunt further
to find one that is strong enough to preserve the shells permanently. I
have found one at 45%, but have been advised that Polish vodka is stronger
so I will try to track some down.

Sarah Longrigg

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