Written by Lu Allington-Jones, Senior Conservator, and Wren Montgomery, FTIR Specialist, both at the Natural History Museum, London
One day, not so very long ago, a request came into the Conservation Centre at the Natural History Museum (London, UK) to investigate why some fragmentary limb bones of a hadrosaurian dinosaur had been wrapped in a polythene bag marked “Danger, Asbestos Hazard”.
Asbestos is present in many mineral collections, and often social history collections – it’s fire-resistant properties were once exploited to make things like clothes and fire blankets. We even have Benjamin Franklin’s asbestos purse on display in our beautiful mineral gallery (not sure why Ben needed a fire-proof purse but never mind).
So, why would asbestos be in a fossil? Historically gap-fills have been created using many rather bizarre substances including, apparently “asbestos-mâché” and it is not hard to imagine that asbestos fibre could have been added to a plaster of Paris gap-fill when it was used frequently in artex ceilings up until the 1980s. The asbestos fibres were added to the mix (before people realised the health risks) to aid flexibility and tensile strength and to reduce shrinkage. For the same reasons we now add glass fibre to epoxy resin casts or supports.
So this is what was inside the polythene bag:
Further investigation of the storage tray brought to light a small glass vial containing white fibres which were also analysed using FTIR. They proved to simply be polystyrene.
So…no asbestos, yay! But where did these polystyrene fibres come from? Lu then remembered re-storing a particular specimen when she first started working at the Museum almost 20 years ago: a fossil had been embedded in a support made of polystyrene. Rather than cutting out the depressions, someone had dipped the bones in acetone and briefly pressed them into a thick sheet of polystyrene to make contoured indents (not something that would be done now because the polystyrene can stick to the specimen). The same treatment must have been done to these dinosaur bones, and the dissolved polystyrene must have made strings (like melted cheese) which hardened as the bones were pulled away. The polystyrene mount must have been removed subsequently and replaced with a Correx® tray lined with plastazote. This project certainly shows the importance of keeping records! But at least it turned out to be a fun mystery to solve. Since we also tend not to use Correx® anymore, because it can become brittle and crumble over time, this project has made me wonder about the materials that I use now – will future me’s look back and scoff?
In the comfortable knowledge that the specimen is not in fact hazardous, it was repaired. This was undertaken using 40% Paraloid B72 in acetone which was bulked with glass microballoons pre-tinted with earth pigments. A support was created for the repaired limb bones using Epopast 400, lined with plastazote foam, which allows them to be stored and handled without risking damage. All treatments were then recorded on the digital collection management system!
For more on epopast supports see:
For more on hazards in collections see:
Collections Trust. 2016. Hazards in Museum Collections. https://collectionstrust.org.uk/wp-content/uploads/2016/11/SHARE-Museums-East-How-To-Guide-to-Hazards-in-Museum-Collections.pdf
Freedman, J. (2012). Safe Storage and Handling of Potentially Hazardous Minerals in Natural History Collections. NatSCA News, Issue 22, 51 ‐ 65.https://www.natsca.org/article/112
More on the Gallery 30 Project:
Cornish, L., Doyle, A. and Swannell, J. 1995. The gallery 30 project: Conservation of a collection of fossil marine reptiles. The Conservator 19(1): 20-28. https://doi.org/10.1080/01410096.1995.9995090