Conservation teams in museums take great care of collection objects: their job can involve cleaning objects to get them ready for an exhibition, carefully installing them in a gallery display, or caring for them when they’ve suffered from the damages of time. But even when objects are sitting still behind a display glass, away from prying fingers or any exterior contamination, temperature and humidity are some of the invisible factors that conservators must keep in mind to preserve objects.
Getting environmental conditions right and to a consistent level is extremely important when caring for a collection. Too much humidity can create the perfect environment for mould to grow: too low, and objects can shrink and crack. The same can be said about temperature: if it rises too high, collections accelerate decay and wax objects can melt. On the other hand, in low temperatures objects can be put under stress and become brittle. Most paintings require a stable environment at around 40-60% relative humidity (RH). For metals, a relative humidity of under 65% in a clean and dry environment is recommended, as moisture and salts can stimulate corrosion.
To prevent this, regular monitoring of humidity and temperature is necessary to keep an eye on any big changes. Conservators use a tool called an environmental monitor, or a Hanwell monitor: these are small data loggers that measure the relative humidity and temperature of a room. Hidden around the museum, they provide conservators with information that help keep our collection safe.
The monitors alert conservators to the environmental conditions of the room and, if necessary, changes can be made. For example, if the humidity in a showcase is too high, silica gel can be added to absorb excess moisture and make the humidity suitable for the collection.
This ensures that they give as accurate a reading as possible. Certain loan objects require more frequent monitoring – for example once a week or month, and the data is analysed and recorded.
The Science Museum has 99 monitors, and each one needs to be adjusted individually. This is done by putting the monitors into three different humidity calibration salt chambers (low, medium and high). These are left for one and half to two hours in each humidity chamber and the raw data recorded in Hanwell’s software system called EMS (Environmental Management System). Once the process is completed the monitor will be accurate to within 3 percentage points above or below and returned to its place in the museum.
Environmental monitoring is a small but essential part of the work done by the conservation team to preserve objects from our collection: you can find out more about other tasks carried by our conservators on our blog, from pest management to repairing and transporting fragile objects.