[NHCOLL-L:268] Re: molluscan periostracum -Reply

[Sally Shelton]

Both the problems described--periostracum delamination and
Byne's "disease"--are associated with high and fluctuating
RH levels. The paraffin wax-xylene treatment for the former
may very seriously compromise the periostracum tissue as a
present or future source of biochemical analysis. This
sounds like a variation on the old amateur standby of
coating all shells in a mixture of mineral oil and lighter
fluid, the oil to penetrate all the pores and the
hydrocarbon to facilitate rapid carrying and drying. It's
not something recommended for research collections in any
way. The only other incident I've seen using paraffin was a
well-intentioned effort to coat some fragile fossil bones so
that they would not get water-logged in a specific gravity
study. Of course, they became wax-logged instead, which was
even harder to deal with, and there they sit today, waxed
and unavailable for further bio/geochemical work. 

It is far preferable to deal with either/both of these
problems through microclimate control than through
irreversibly coating the specimens. With active Byne's, a
low RH will drastically slow the reaction (no reaction ever
truly stops). The shells should not be nested in, or in
contact with, the silica gel or other desiccant. There are
several designs for creating desiccant chambers, from small
boxes to active systems for whole steel storage cases. The
same approach can help the periostracum delamination
problem. Check out the papers in section IV of the _Storage
of Natural History_ volume edited by Rose and de Torres,
published by SPNHC. (If you are not in a naturally arid
area, you probably can't and don't want to bring a whole
room down to 40% or less RH.) 

The paraffin wax is pretty inert, but the xylene is
something to be used with respiratory and skin-exposure
safeguards. In coating something, you're limiting the
options for its research use down the road, as biomolecular
and chemical techniques get more sophisticated and the
scientific value of pristine material rises. Just be aware
that that's the tradeoff you're making.

Cheers,
Sally Shelton
Collections Officer, NMNH
Smithsonian Institution