Vacuum in the Museum

Organic materials decay. Those that have already existed for thousands of years even more easily. A special treatment using vacuum, provided by vacuum pumps from Busch, helps make sure that freshly excavated wooden archaeological finds can be preserved for generations to come.

The discovery of an artifact from thousands of years ago, still perfectly preserved, is an archeologist’s dream. However, without the proper care and attention, finds made from organic materials can decay rapidly once brought to the surface. But there are ways to stop these chemical and structural changes in their tracks, allowing the pieces to be studied at leisure and safely put on display in the museum.

The preserving power of water

Remnants of wooden Viking ships are still being discovered today, but due to their seafaring nature, are often found in water. Although this makes conditions challenging during excavation, the location is something of a blessing to archaeologists. Water can cause a lot of damage, but it can also preserve. On land, the same wooden piece would have long since rotted. The water helps keep wood intact for much longer, as do the mud and sand that have covered the find in the years since it made its way to the sea floor. However, this can be quickly undone when the artifact is brought onto land. Cellulose breaks down in water and makes wood very porous and sponge-like. It will keep its shape as long as it stays wet, but when exposed to air, the excess water will evaporate. The cell walls will collapse, shrinking and distorting the piece. So, before a wooden find, such as a fragment of a ship, can be further examined and displayed, it needs to be correctly preserved.

Stabilizing with wax

One way of stopping the decay is with the use of polyethylene glycol (PEG), a type of synthetic wax. The still-waterlogged piece is soaked in liquid PEG, which penetrates all the nooks and crannies in the wood and stabilizes the wood cells. The item is then wrapped in foam rubber and frozen to -20 °C, hardening the wax. As well as stabilizing the object’s structure, the wax also has the advantage of preventing ice crystals from forming, which could cause further damage. Then, vacuum pumps from Busch are used. The combination of vacuum and low temperature causes the now-frozen water to sublimate, changing from solid ice directly into water vapor, without becoming liquid again. The vapor is immediately extracted by the vacuum pumps so that the item does not have the chance to rehydrate. At the end of the process, only the waxy wood is left behind. The process is long, taking over three months, but leaves the find completely dried and stable, and ready to be exhibited.