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

Fri May 19 05:47:13 EDT 2017

This is somewhat dependent on whether the shells are to be displayed or not.  As Christian says, if you treat them, then molecular biologists may find them contaminated with chemicals.

However, I would urge that a few (the worst maybe?) could be treated to see how the periostracum responds and I would use Bollmann Ultra-Soft, normally used for mammal skins - but it has a host of other effective applications, and is available from WASCO.  Just brush a little on (shake the bottle first!) and see whether you get an overall improvement - the effect takes a few hours or overnight to take effect.

With all good wishes, Simon.

Simon Moore MIScT, RSci, FLS, ACR
Conservator of Natural Sciences and Cutlery Historian,
www.natural-history-conservation.com 

On 19 May 2017, at 10:27, Christian Baars <Christian.Baars at museumwales.ac.uk> wrote:

> 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=dvKV-_JbQhLXKNkY4nR7Qr_U61VQE6FMy1P4RUavXdg&s=-WiV2a0iw7vJEp8lrWXjON9Zuuur8lSEX2nmHmp684I&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
> 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=dvKV-_JbQhLXKNkY4nR7Qr_U61VQE6FMy1P4RUavXdg&s=YA2SSWI4DEHC_Eb6CkbwisdHEOQmOLbd-Z10esVK_ws&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=dvKV-_JbQhLXKNkY4nR7Qr_U61VQE6FMy1P4RUavXdg&s=XxyV4O7X2uHcZJy2RjmbihYojleGZjZYA3m4To1dSPo&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 Tel 215-405-5096 - Fax 215-299-1170
>  
>  
>  
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