In this special feature, project Conservator, Esther Sharp takes us through the many conservation challenges of putting on the ‘Darwin the Geologist’ exhibition from emptying out the objects that used to be housed in Bays 1 and 2 where the exhibition now is to deciding what should be displayed and how.
The redevelopment of Bays 1 and 2 of the Sedgwick Museum gallery gave the collections staff an unusual opportunity to look at, handle, and assess the condition of a large number of objects in the museum collections. As previously reported, for the new exhibition to be installed, almost 800 specimens had to be removed from display to long term storage. If there was anything seriously amiss, these specimens could be conserved before entering storage.
Similarly, 2000 rocks collected by Charles Darwin were examined to see whether their condition was good enough to display in the new exhibitions. Each rock destined for display was examined, and its condition and display requirements were assessed. This meant that the exhibition would not endanger the long-term survival of any of the specimens.
There were relatively few specimens removed from display which required conservation attention. Often, moving specimens out of tightly packed exhibits was all the improvement that was required to improve their long term survival. Specimens were packed in conservation-grade boxes lined with inert foam and tissue. In some cases custom made boxes were necessary to accommodate unusually shaped specimens.
Many of the specimens were very dirty, and these were cleaned using a soft brush. Cleaning is one of the most important aspects of conservation, because it removes harmful contaminants, enables any damage to be inspected and can reveal pest infestations.
In the past, if a specimen had broken it would be normal to repair it with adhesive. These adhesives often have a limited life and can fracture, leaving the specimen broken, but not necessarily along the original fracture as glues can set up stresses in specimens such as mammoth teeth.
In this situation we would rarely try to repair the broken object. If the old glue looks in particularly bad condition we might try to remove it and consolidate any fragile areas. Otherwise the best choice for the object is to leave it in two parts. If the specimen is required for exhibition, or will fall apart entirely then the two parts might be reunited using a reversible conservation grade adhesive.
Other than the new exhibition itself, one of the most striking changes in the gallery has been the move of the ‘Giant Elk’ to its new display in Bay 3, which we reported on in an earlier blog. Because it is out in the open in the gallery the giant deer gathers dirt quickly, and this provided and excellent opportunity for a really thorough clean.
However, when the head was examined prior to lifting off its mount, a large crack was noticed in the right set of antlers, caused by some prior damage. To prevent further cracking, the damage was repaired using a mixture of conservation grade reversible adhesive and tiny glass balloons. This forms a repair that can be removed in the future, if required. The mixture can also be painted to match the original bone.
One of the more unexpected finds in the displays was that of a cow scalp, complete with horns, which was displayed on a wooden mount. When examined closely we noticed evidence of clothes moths within the fur. While the moths appeared to be dead, we could not risk transporting a potentially damaging pest such as clothes moths into our storage facility.
Luckily we had a solution here in Cambridge. The best way to eradicate an insect pest within specimens such as this is to freeze it. The Scott Polar Research Institute allowed us to place our specimen into its minus 40oC cold room for 7 days, which was certain to destroy anything which might be living on it. It was then safe to take the specimen to our climate-controlled store, knowing that we would not be infesting our stores.
As well as specimens collected by Charles Darwin, the exhibition contains a number of unusual plaster casts of fossils, made in the mid-19th Century. The largest of these is the pelvis of the extinct ground sloth Megatherium. This cast was purchased by Adam Sedgwick for his museum, and is redisplayed here for the first time in over 100 years. Made of painted plaster the specimen had been chipped quite badly in places and was dirty from being stored for years in rooms heated by coal fires.
Some of the soot and grime was removed using a special rubber sponge, designed to remove soot. It was not cleaned completely, as this would have removed some of the character of the specimen. Holes were repaired using adhesive and glass microballoons (as for the giant deer), and in the case of one large hole, using special conservation paper and paints.
The Importance of Climate
As well as undertaking conservation on specimens which are broken or damaged (which is called remedial conservation), one of the conservators most important tasks is to ensure that objects do not deteriorate in any way. Sometimes a specimen in perfectly good condition can be stored or displayed in a way which causes it damage. Preventing this from happening is known as preventative conservation.
Preventative conservation can often be achieved by controlling the climate the specimen is kept in. Certain environments can be damaging for different types of specimen. Paper must not be kept too dry or it will become brittle. If it is too damp it might become mouldy or encourage other pests to eat the paper or ink.
Preventative conservation can be quite simple to achieve in some cases. It might simply be keeping the object out of direct sunlight. However sometimes it can be more difficult to achieve, and require complicated equipment such as air conditioners or humidity control.
If you look around the Darwin the Geologist exhibition, you will see that some cases have lower light levels in them than others. Those with low light levels contain objects which are vulnerable to too much light, and whose colours might be affected or faded by it. One example is the Geological Map of North Wales, which belonged to Adam Sedgwick.
This map was hand-coloured by Sedgwick to represent the different geological strata. If you look closely you can also see hand-written notes, made by the previous Woodwardian Professor himself. In order to prevent any damage occurring to this map, the case must be kept to a low light level. Ideally, delicate printed or written matter should be kept at 50 Lux (a unit of light intensity) or lower. To compare, full daylight without direct sun can measure up for 25,000 Lux.
You will see that there are also very low light levels in the reconstruction of Darwin’s Cabin. This is because it contains one of Charles Darwin’s own field notebooks from the Voyage of the Beagle, and must therefore be protected from too much light.
Another way in which we control the environment of a museum object is through regulating the temperature and relative humidity. Relative humidity (%RH) refers to how much water is present in the air, relative to the maximum amount of water that air could hold at a particular temperature. If the relative humidity is too high, materials like wood and leather will grow mould and rot. Rocks such as meteorites can rust as they sometimes have a high iron content, and specimens containing iron pyrites can begin to decay and break down. If the relative humidity is too low, some bones and organic remains will crack and fall apart. We have to find a relative humidity level that is a best compromise for an exhibition which contains a mixed collection of objects.
If you look in some of the cases you will see small boxes with antennae on top of them. This is part of the Msuem’s environmental monitoring system. The boxes (transmitters) are radio controlled and send data back to a computer in the Museum. The conservator analyses this data to assess the environmental conditions in the Museum. During the Darwin project this system was extensively upgraded.
Our exhibition contains three humidity controlled cases, which house particularly fragile objects. The Darwin cabin reconstruction contains a case which houses Darwin’s notebook, his horn-rimmed lenses and pistol, as well as two other scientific instruments. Darwin’s Wollaston medal, awarded by The Geological Society of London is also kept in a small humidity controlled case, to protect it. Finally, our largest humidity-controlled case houses the reconstructions of the desks of Robert Brown and Alfred Harker.
Unlike the other two cases, this case is in place to protect some of the most delicate rocks from the Beagle Collection. Fossilised wood can be particularly vulnerable to high or fluctuating relative humidity, and Robert Brown’s desk reconstruction contains some of the fossil wood which was collected by Darwin, and sent to Brown for identification. This case is stabilised to 45% relative humidity, which prevents any iron pyrite which is may be present in the fossil wood from breaking down due to too much moisture in the air.
In some cases, a specimen might be so fragile that it is not possible to put it on display. A regular visitor might notice that the museum can change temperature between visits. Because the display cases in the gallery are the original oak and mahogany cases, dating back to the opening of the museum in 1904, it is very difficult to completely control the climate inside them. The cases, while beautiful and an integral part of the character of the Museum can’t be easily adapted to do this. This means that some specimens simply cannot be displayed without the risk that they will break down and be destroyed.
This specimen, which bears one of Darwin’s original labels from the Beagle Voyage, is very crumbly and fragile. Exposure over the long term to fluctuating environmental conditions could cause it to disintegrate.
Some specimens are just too physically fragile to be displayed, and the vibration from footfalls in the gallery and traffic in the street might cause them to fall apart. This specimen bears tiny crystals on its surface, but they are so fragile that even touching the rock causes them to fall off.
Despite the fact that we could not display all parts of the Beagle rock collection in the exhibition, the Darwin the Geologist website will have photographs and detailed information about all the rocks in the Beagle collection, making the entire collection accessible, despite its sometimes fragile condition.
All the specimens housed within the Sedgwick Museum’s collections are of importance, but some are more vulnerable to damage, decay or disintegration than others. Part of the job of the Conservator is to assess the collections and take measures to halt any decay and prevent further damage occurring. With 1.5 million specimens in the Sedgwick’s collections this is not a small task, but ‘Darwin the Geologist’ has presented the opportunity to focus on a relatively small part of the collections, assess its condition and act accordingly, to ensure its long-term survival.