The next exciting new chapter in our ‘Once in a Whale’ conservation project involves the re-articulation of the cetacean specimens. This includes (where appropriate) removing old, corroded wiring from between bone and cartilage joints, consolidating the bone and re-articulating the skeletons with new wire. This blog entry gives an insight into this process and our experiences gained so far.
Consolidation and repairs
Once the bones are individually removed, we assess their structure and strength. The specimens appear to be extremely varied in both their texture and structural integrity. Some skeletons are more friable and brittle than others, which could be due to variety of reasons, including their age or initial method of preparation. Unfortunately, we have no record of the latter.
Where bone surfaces are more fragile, we are consolidating the bone with Butvar B98 (polyvinyl butyral (PVB) resin ) in ethanol. This consolidant was selected for its binding efficiency combined with flexibility. With a reasonably high glass-transition temperature (Tg) of 62-68 °C, as well as favourable results in UV, light and heat exposure studies, Butvar B98 was deemed suitable for use on these specimens, as it would survive exposure to the environmental extremes of the museum’s roof space. It also dries with a matt finish to look natural against the bone.
While very high UV conditions may cause cross-linking of Butvar B98, leading to an insoluble network (Horie 2010, P.145-7), we felt it’s application was justified. Although we won’t be able to remove it entirely in the distant future, it will ensure the survival of these specimens for decades to come and thus allow them to continue to serve their purpose as display specimens in the museum. We are applying the consolidant by injection into pores in the bone, or by painting directly onto the surface.
Fractures in the bone, are being re-adhered with Paraloid B44 (ethyl methacrylate co-polymer resin) in acetone.
While Paraloid B72, a Feller Class A material, has excellent ageing properties, its Tg is only 40°C. Working with the same group of resins, we selected Paraloid B44, which due to a slight composition ratio variation, has a Tg of 60°C (Horie 2010, p.159-160) and is therefore more suited to our museum environment.
Challenges and opportunities
We thought we had a dilemma on our hands when some of the old, corroded copper wiring had become stuck, particularly in cartilage joints, causing the wire to snap during attempts to remove it with pliers. Who knew what nuggets of knowledge entomologists have when encountered over a cup of tea in the staff room? When faced with mounted insects, whose metal pins have developed verdigris, entomology staff at OUMNH run an electric current through the pin to heat it, thus slightly melting remaining fats in the insects’ body, allowing the pin to slide out of the specimen.
We tried the method first using a battery, before being presented with a soldering iron- which worked like magic- just heating the copper wire sufficiently, to slightly melt the surrounding cartilage, enabling the wire to be pulled free. It really helps to talk to colleagues about your work- you never know what ideas and gadgets they may have!
While the bones guide the re-articulation process to some extent (e.g. spacing of ribs), working on intuition has not always proven anatomically accurate. Sourcing reliable reference material has also been surprisingly challenging. Questions such as: how inflated should the rib cage be? At what distance from the vertebrae should the floating pelvis hang? How should phalange digits be spaced and how many bones were there originally?
To answer some of these questions, we have been in touch with a number of specialists, from Alaska to Scotland. Slowly the information we need is being assembled, allowing us to articulate our specimens as accurately as possible.
While we conservators feel to some extent protective over our own ‘adopted’ specimens, this project stage encourages us to work together. Given the size and weight of ribs, sternums and skulls etc. we rely on each other to help position, support, check for symmetry and tighten joints made.
Work in progress
Ribs- The Bottlenose Dolphin’s (Tursiops truncatus, Montagu, 1821) ribcage was crying out for re-wiring and re-shaping and to ensure its preservation and improve its scientific accuracy. Following the dismantling, consolidation and re-assembly with new wires, its shape was improved and strengthened with an additional wire cross-link at its widest point, the 7th rib (Post, 2012).
Skull- While rewiring the Bottlenose Dolphin skull, we took the opportunity to open the mouth slightly, partly to ensure its teeth didn’t abrade each other as well as to allow visitors to study the teeth in more detail. Doesn’t he look happy now?
We are under continued pressure to complete our ‘Once in a Whale’ conservation project before the scaffolding is due to be taken down, following the completion of roof repairs. Alongside that, we also have pieces of a Humpback Whale ((Megaptera novaeangliae (Borowski, 1781)) skull to address- check out our next blog entry, to see our enormous challenge ahead!
- Horie, V. 2010. Materials for Conservation. Organic consolidants, adhesives and coatings. 2nd edition. London: Butterworth-Heinemann.
- Post, L. 2012. The Whale Building Book. A Step-by-Step Guide to Preparing and Assembling Medium-sized Whale Skeletons. Self published.
Gemma Aboe, Assistant Conservator
Reviewed by Bethany Palumbo, Conservator of Life Sciences