[Nhcoll-l] To oil or not to oil?

Fri May 19 05:27:54 EDT 2017

Paul,

What you describe almost appears to be a loss-loss situation: treat the shells and lose the potential for chemical analysis, don't treat and lose the potential for morphological description.

I am no malacologist, but the beauty of this forum is that it brings together so many disciplines and perhaps I may be able to contribute from an 'outsider's' point of view.

Various materials require different storage environments. For some collections it has been accepted for decades that it is impossible to keep all materials making up a complete collection in the same room under the same conditions. Think archaeology, excavated iron objects are so sensitive to corrosion under 'normal' museum store conditions that they are usually packaged in microenvironments at, ideally, <10% RH. We treat geological specimens containing ferrous sulphides in a similar way.

If your mollusc shells would benefit, i.e. suffer less damage, from being stored at higher RH, have you considered storing them in a microenvironment at high RH? We are in the fortunate position to have a naturally cool and damp room in the sub-basement of the museum building, where we have been storing a number of minerals (for example, polyhydrated sulphates) successfully (i.e. without any damage through dehydration) for several years. But you can also create microenvironments using saturated salt solutions (see, e.g., Greenspan 1977 https://urldefense.proofpoint.com/v2/url?u=http-3A__nvlpubs.nist.gov_nistpubs_jres_81A_jresv81An1p89-5FA1b.pdf&d=DwIF-g&c=-dg2m7zWuuDZ0MUcV7Sdqw&r=CLFZJ3fvGSmDp7xK1dNZfh6uGV_h-8NVlo3fXNoRNzI&m=VKQZS6rxG5AJQtsXndEVaqcOUPV6kSpvLi_1WDMi92I&s=r2Se_10ri0OGGh5AMJyd6j525aZxVXTjb91VjhmJEbE&e= ). There is a question of long-term maintenance, of course, as with any micro environmental storage. Another concern may be the potential for mould growth, and perhaps the potential for small salt deposits being precipitated on specimens. I have not tried it but it is on my to-do list to find some answers to these questions. If it worked for your shells you may have a way of preserving both morphological and chemical integrity of your specimens.

Kind regards
Christian

Christian Baars PhD AMA
Senior Preventive Conservator
National Museum Cardiff
Department of Collection Services
Cathays Park, Cardiff CF10 4NP, UK
Telephone: +44 (0)29 2057 3302
E-mail: christian.baars at museumwales.ac.uk<mailto:christian.baars at museumwales.ac.uk>
Twitter: @NMWPrevCons
Blog: https://urldefense.proofpoint.com/v2/url?u=http-3A__www.museumwales.ac.uk_blog_-3Fcat-3D2484&d=DwIF-g&c=-dg2m7zWuuDZ0MUcV7Sdqw&r=CLFZJ3fvGSmDp7xK1dNZfh6uGV_h-8NVlo3fXNoRNzI&m=VKQZS6rxG5AJQtsXndEVaqcOUPV6kSpvLi_1WDMi92I&s=J99x1LDnP1YF3_PDZ5Bd7KnXO91DDpB7djVp_TAu3Z4&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__museum.wales_staff_643_Christian-2DBaars_&d=DwIF-g&c=-dg2m7zWuuDZ0MUcV7Sdqw&r=CLFZJ3fvGSmDp7xK1dNZfh6uGV_h-8NVlo3fXNoRNzI&m=VKQZS6rxG5AJQtsXndEVaqcOUPV6kSpvLi_1WDMi92I&s=ZLCZJZZSEjP3XfhWT-9TjH2LFCkgZeeU_fHg6C3zO3g&e= 

From: nhcoll-l-bounces at mailman.yale.edu [mailto:nhcoll-l-bounces at mailman.yale.edu] On Behalf Of Callomon,Paul
Sent: 18 May 2017 19:49
To: NH-COLL listserv (nhcoll-l at mailman.yale.edu) <nhcoll-l at mailman.yale.edu>
Subject: [Nhcoll-l] To oil or not to oil?

(This question is mainly for the managers of mollusk collections, but I'd like to hear from others who might encounter a similar quandary)

The shells of certain mollusks (almost all true mussels [Mytilidae]; pearl oysters [Pterioidea]; pen shells [Pinnidae] and many freshwater mussels) are composed mostly of nacre and have a thick, bonded periostracum. Removed from the water and placed in a dry environment, they begin to crack and split in a fairly short time. Their nacre can also decay, becoming powdery and weakening with time. The periostracum dries and hardens, and as its modulus of expansion differs from that of the shell, it begins to flake off or - in  the case of thinner shells - to crack the shell. Maintaining humidity at 45-60% year-round should slow this essentially evaporative process, but is unlikely to stop it.
A traditional technique to guard against all this is to coat the shells inside and out with a film of mineral oil (Petrolatum). This slows the escape of moisture from the shell matrix and keeps the periostracum somewhat flexible, and it certainly works; here at the Academy we have oiled freshwater mussel specimens dating back to the 1850s that remain entire. However, oiling is an additive technique and not fully reversible; detergents can remove the surface film but not purge the shell of oil entirely.
The debate, then, is as follows: On the one hand, adding a hydrocarbon to the shell might inhibit or preclude future chemical analysis techniques that we have not yet developed. On the other, a great deal of work in the mollusca (and many other groups) is based on morphology, and a tray of dust and fragments is of little use in that regard.

So: in your collection - to oil or not to oil?

Paul Callomon
Collection Manager, Malacology, Invertebrate Paleontology and General Invertebrates
________________________________
Academy of Natural Sciences of Drexel University, Philadelphia
1900 Benjamin Franklin Parkway, Philadelphia PA 19103-1195, USA
callomon at ansp.org<mailto:callomon at ansp.org> Tel 215-405-5096 - Fax 215-299-1170

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