A Very Delicate Skull

Things are moving along quickly and we have almost completed cleaning the Sei whale skeleton.

However, the skull on this skeleton requires a lot of careful and painstaking work. The cranial bone has deteriorated considerably is now extremely thin and delicate. In addition there is a lot of exposed trabecular bone (the honeycomb like bone found beneath the smooth surface bone). This makes cleaning the bone very difficult as we do not want to damage it any further.
This picture shows how paper thin some of the bone on the skull is.





There is evidence of past repairs to the skull as there are thin strips of bone, that appear to have fallen off, screwed back onto the premaxilla, often with small wooden supports added. We have also discovered fragments of bone lying in the skull which have fallen off the maxilla, vomer and nasal bones.

Gordon has been tackling the skull and has modified our usual cleaning methods to work in this area. In order to clean the very thin bone he applied a solution of ammonia with a soft brush to the bone surface, left it for 5 minutes and then using the soft bristled brush gently foamed the solution on the surface, lifting the dirt. This was then removed either with a vacuum cleaned or with tissue paper to blot off the excess, so that no rubbing or scrubbing was required.

The parts of the pre-maxilla that had previously been screwed back on were removed and carefully stored so that they can be re-attached more sympathetically later on in the project. All the small fragments we found were glued back into place (a bit like doing a whale skull jigsaw puzzle). This was achieved using a special conservation 'glue'called paraloid (acryloid) B-72. The important thing about paraloid is that it is 'reversible' - that is, it can easily be removed in the future using acetone. The use of non permanent 'glues' is an important aspect of conservation as it means you can repair a specimen with the possibility of non destructive change if necessary in the future.

The paraloid was used in combination with Japanese tissue paper to stick the paper thin bones together. The tissue paper was used as a reinforcing agents as the edges of the bones were just too thin to stick to each other.

Here are some pictures of the Sei whale as it is being cleaned....

The Sei whale skull work is nearly completed and the team are moving onto the Humpback whale - once again we have found a name - Roger!

Forskningsdagene

It was a very busy Sunday for Bergen University as it hosted a Research Day (Forskningsdag) for the public. There was a busy schedule of events - from mummifying a hen to getting oil from a stone. The whale project was included and people could come and visit us here in the Whale Hall, climb the scaffolding and get up close and personal with the whale skeletons.

Despite the very stormy weather we had around 100 visitors in just 3 hours so the whale team was very busy showing people around and answering questions! We hope everyone enjoyed seeing the skeletons and the Museum project in action.

Laser Cleaning

Laser Cleaning

Whilst experimenting with cleaning methods we gave laser cleaning a go.

Laser cleaning is becoming increasingly popular in conservation, particularly when dirt needs to be cleaned from very delicate surfaces such as textiles and paintings. The most commonly used laser cleaning systems in conservation emit short pulses of light, typically at a wavelength of 1064 nm or 532 nm. Light at this wavelength quickly and selectively heat the dirt on the surface, which expands and comes away.

In many cases, the light interacts only weakly with the surface of the object and the removal process stops as soon as the clean surface is exposed due to colour differences between the dirt and the surface. It is, therefore, possible to completely remove unwanted layers without over cleaning the valuable surface. This type of cleaning could be very useful for areas of bone that are very fragile and a method that did not ‘touch’ the surface and cause further damage would be advantageous – such as the underside of some skulls which has begun to peer away.

Although this cleaning method is often used on stonework and paintings there is very little research about it’s effect on bone – so we proceeded with caution and started our tests on some objects that had been up in the attic and were not of scientific importance. We chose items that would be very difficult to clean with traditional methods and so would be good subjects for laser cleaning. We had mixed results – in some cases it was very effective and removed dirt from surfaces that would otherwise have been awkward to clean. However, occasionally the laser failed to remove much dirt, or caused a change in colour of the original surface.

This may have been because lasers do not work on dark materials with lighter dirt cover - only the other way around! That's why lasers are often great for cleaning light \ greyish sandstone and marble with a black crust and that's exactly why we thought it could work on our bone material. Small tests have shown that dirty bone surfaces (without oil!) are easily and effectively cleaned with lasers.

Examples of laser cleaning: Swan feathers; the spikey skin of a flat fish; coral

As you can see the laser removed the dirt from the feathers but also discoloured them - making them yellow. The flat fish and coral however were successfully cleaned.

We then tried the laser on the stable surface of jaw of ‘Finn’, the Sei whale’s. The results however were not all we had hoped for. The laser did not damage the bone or change it’s colour which was positive but nor did it remove much of the dirt!

Laser cleaning the mandible of the Sei whale

It wasn’t as effective as using ammonia or a water and detergent. So, although we had fun experimenting with the laser cleaner and managed to clean some usual objects that otherwise would have remained dirty it wasn’t going to be a useful tool for the whales.

A square of oily whale bone after laser cleaning. Although some material has been removed dirt and grease remains on the surface.