Behind the Scenes of the Fluid Collection

By Claire Smith, Project Officer at the Cole Museum of Zoology


As you may know, the Cole Museum of Zoology is closed at the moment, while we prepare to move our collections into the new Health and Life Sciences building. Each week on Twitter, I share a thread about the progress that the fluid preservation team have been making towards the move. Here, I can give you a slightly more in-depth look at the kinds of decisions we need to make as we carry out this work.

Our next specimen coming into the lab is Cole 1338, a developmental series of the electric ray. It’s labelled Torpedo ocellata, but this species is now classified as Torpedo torpedo. It’s been in storage for a number of years, and we need to get it ready to go out on display in the new museum. It arrived at the Cole museum in 1921 from the Naples Marine Biological Laboratory along with a number of other specimens. These were all prepared by Salvatore Lo Bianco, a renowned preparator of marine species. The researchers in Naples specialised in embryology, and this particular specimen is an excellent example. It shows fourteen stages of development, from the blastoderm through to the fully formed embryo.

As you can see, the level of the fluid is not at the top of the jar – it’s dropped due to evaporation over time. The specimen is maintained in an alcohol-based fluid, Industrial Methylated Spirit (IMS). Because alcohol evaporates more quickly than water, the IMS gradually becomes diluted. As a result, we need to check the fluid and make sure it remains at the right strength to keep the electric rays in good condition. We do this by carefully removing the bung, and testing the fluid with an alcohol density meter. If it measures between seventy and eighty percent alcohol, we can simply top it up with more of the same strength. If it measures less than seventy percent, we’d have to replace the fluid completely. We do this by increasing the percentage in stages. This helps to prevent the delicate specimens from cell damage, which can be caused by raising the percentage of alcohol too quickly.

The bitumen sealing the lid has also started to crack – not surprising, given that it’s ninety-nine years old! We’ll carefully remove the lid and clean off all the bitumen, then we’ll re-seal the jar with silicone. We don’t use bitumen to seal our fluid specimens – it gives off harmful fumes when heated, and is no longer considered safe to use. We’ll also replace the porous cork bung with a silicone one, to keep any future evaporation to a minimum.

With any object that we need to work on, our aim is to intervene as little as possible, while still ensuring that the specimen will remain in good condition over a long period of time. In particular, we try not to take delicate specimens such as these out of their glass jar, as removing them from the supporting fluid can cause damage. We also need to consider whether any of our changes will have an impact on Lo Bianco’s original preparation.

In this particular specimen, the glass plate on which the electric rays are mounted has been backed by a piece of black wood. This allows them to be clearly seen, although it’s more common for the outside of the jar to be painted in a dark colour.

In bitumen sealed jars such as this one, the glass mounting plate is almost always stuck to the lid at the top corners. When we re-seal the lid of the jar with silicone, we don’t re-attach these corners. We try not to have any sealant on the inside of the jar, as prolonged contact with the fluid can eventually cause leakage. The layer of silicone will also be thinner than the bitumen, which leaves the backing plate extremely close to the lid of the jar. This risks compromising the seal, which is a common cause of evaporation. Usually we would solve this problem by trimming away a narrow strip of glass from the top of the backing plate, but that would mean removing the extremely delicate rays from their jar.

We also need to consider the wooden backing, which is quite unusual. If the wooden panel is something which is characteristic of Lo Bianco’s preparation work, we would need to think carefully about altering it, or even removing it and painting the back of the jar instead. Whatever decision we reach, we need to make sure that we’re balancing the integrity of the original preparation with the necessary techniques to keep the embryonic rays in good condition for as long as we possibly can.

You can find out more about the Cole Museum of Zoology on our website, including how to volunteer with the collections yourself when we re-open. For all the latest news about our move to the new Life Sciences building, it’s best to follow @ColeZoology and @ColeMM2019 on Twitter. For weekly updates about the practical work involved in fluid collections, you can take a look at @wetconservatrix.