Over time, the fat can ooze out of cetacean skeletons on display or in storage. The oils that accumulate on the surface eventually start to oxidise and cross-polymerise and coat the bones in a waxy surface layer that can resist even many organic solvents. The interior fat will degrade over time, making it harder to extract. The degraded fats can also harm the bone. A 27m long blue whale collected by the Museum in 1918 has degraded so badly that only the mandibles (jaw bones) now remain.
In the past, cetacean bones were commonly degreased using chlorinated hydrocarbons like trichloroethylene or alkanes like petrol. These chemicals are highly toxic or highly flammable, which makes working with them difficult and dangerous.
Researchers have been working for many years to solve this issue that causes problems for the South Australian Museum and many other museums around the world. David Stemmer, Collection Manager, Mammals, is investigating a new degreasing technique with the potential to significantly improve the preservation and display of cetacean skeletons.
In 2002 when David joined the Museum team, he began working with a commercial chemist to investigate a range of benign chemicals for degreasing bones. They concentrated on glycol ether surfactant compounds which are used in semi-aqueous cleaning products. These very versatile compounds can mix with water as well as fat and have low toxicity, flammability and vapour pressure. David boiled greasy bones in various glycol ether solutions, but while all glycol ether compounds tested showed some promise as degreasers, several had a detrimental effect on bones and he wasn’t able to develop a workable process.
In 2012, while attending a symposium in France on the conservation of fatty whale bones, David had the chance to talk to solvent toxicologists and other preparators faced with the same issue. As a result, he developed an idea for a new protocol using the glycol ether compounds in a process that does not involve boiling the bones. Results achieved with the new protocol have been extremely promising. The team is now focused on investigating different glycol ether compounds, temperatures and concentrations in order to optimise the technique.
While the ultimate test of degreasing a large whale bone is still to be completed, the team may well be on the way to developing a degreasing technique that is safe, effective, preserves bone integrity and is not too labour intensive or expensive.