Hi Roland, and welcome!

>I collect just
>about everything, every family, species and (almost) every quality, if the
>species is rare or new for me. Of course at some point the problem of space
>will occur, which is probably the only reason to specialise at some point, but
>at the moment there are still a few corners in my flat where I can put another
>cabinet or two.

A man of good sense. My house is full of map-cabinets, with more
(empty!) stacked outdide waiting for another house to fit them
into... I refuse to specialize too much, or to restrict my
collecting...

>And I also have a first question about pinnidae. It seems to be a common
>problem that these shells get cracks after some time. I’ve got a P. nobilis, a
>P. rudis and an unidentified species from Australia – they all show cracks.
>Somebody on this forum suggested some time ago to use oil to prevent breaking,
>I will try this on the next shell but I wonder how this might work. Does the
>oil somehow minimise the tensions in the shell? And how do the tensions get
>in the shell in the first place? If it has something to do with the drying
>process then why don’t other shells break or is there a difference in the
>chemical structure of pinshells?

Pinnids are a pain. They are calcitic, rather than aragonitic, and
composed largely of prismatic crystals aligned perpendicular to the
shell surface (look at a broken edge, you'll see this). They have an
unusually high organic content, and when this dries the shell warps.
When it warps the crystals produce stresses and the shell then cracks.

Treating with some chemical which can replace the water in the
shell's organics (conchiolin) can help reduce or prevent the warpage.
Glycerine is ideal in a way, but apparently is hygroscopic, and may
eventually disappear and allow warpage to begin. Paraffin oil
(colorless, inert) might be the way.

New Zealand's large Paryphanta and Powelliphanta snails are even
worse, the shell being almost entirely made up of periostracum, with
only a thin smear of aragonite within. These, when they die, soon
spit along the sutures and curl up into ragged messes (and it is
liiegal to collect even dead specimens, guarenteeing that if they
become extinct, that there are very few specimens in existence...
needless to say, collectors WILL collect dead ones, so that there are
shells existing when the species are no more). They need to be stored
immersed in glycerine.
--
Andrew Grebneff
165 Evans St, Dunedin 9001, New Zealand
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Seashell, Macintosh, VW/Toyota van nut