Maintaining a stable climate is one of the most important aspects in preserving archaeological materials.
Organic materials such as wood can be very sensitive to environmental changes, especially humidity. If humidity is too high, then bacterial colonies and mould can develop and the conservation agent used to preserve the ship becomes sticky and attracts dust; if too low, then there is risk that the wood will crack and shrink.
We believe that the salt outbreaks on Vasa have developed partly as a result of unstable relative humidity (RH), as the old climate plant could not cope with large numbers of visitors during wet weather. In 2004, the entire plant was substantially overhauled, which maintains the relative humidity around the ship between 51-59% RH.
The temperature is deliberately maintained around 18-20°C. This is a balance between preservation requirement and visitor comfort. It would be better for the ship if temperatures were much lower, as elevated temperatures can accelerate chemical reactions and biological activity.
The Vasa Museum is deliberately kept quite dark. This is because organic materials can be broken down by high and intense light levels, especially light containing ultra-violet radiation. Therefore the light levels in the museum are kept below 100 lux, daylight is not allowed to fall on the ship, and ultra-violet filters have been placed on all the windows.
With more than a million visitors each year, it is not surprising that dust accumulates quickly in the museum. While the public areas are cleaned daily, keeping the ship free of dust is a more complicated job. Twice a year we clean all the upper surfaces of the ship and the rigging using vacuum cleaners and brushes. To reach all of the ship's surfaces, we use the work platform at the stern of the ship, a skylift and the overhead crane.
For more information on the museum's climate control system, read the article Vasa's New Climate Control System by our conservator, Emma Hocker;