Preservation & Prevention
Control of the environment
In an historic building it is difficult to control the heating levels. Temperature affects humidity and so conservators monitor both of these factors in order to determine whether the conditions are damaging to the artefacts and what action to take. Some objects need to be kept in very dry conditions whilst others require damper surroundings. In galleries and stores the moisture content of the air is controlled by dehumidifiers or humidifiers. In smaller confined spaces, for example showcases or storage boxes, buffering agents such as silica gel are used to keep the objects in their optimum micro-climate.
Control of light levels
As explained in the section on Deterioration, light damages objects. Both sunlight and artificial light contain UV, and so have to be carefully controlled. The Museum must make a compromise between exhibiting the objects so that they can be viewed comfortably by visitors yet ensuring that the minimum of harm is done. There are internationally accepted light levels for different museum materials.
Daylight is controlled by blinds and curtains and by applying filtering films to windows and roof lights. Specialist light bulbs and fluorescent tubes have been designed to emit lower levels of UV and these are fitted in most of the galleries. Standard fluorescent tubes are covered with UV filter sleeves. Particularly sensitive objects are provided with individual curtains or covers that can be opened briefly by the visitor for viewing. Some showcases are fitted with timed light switches. Where possible, galleries are kept in complete darkness when the Museum is closed to the public.
Great care must be taken to prevent pollutants from being introduced to the Museum. Some materials, e.g. wood, adhesives, chip board and fabric coatings continually give off pollutants, notably acetic acid, formaldehyde, and sulphur, which are particularly harmful to anything coming into contact with them.
Testing for pollutants is carried out in situ by means of small metal coupons, and 'pollution tubes'. Once monitoring has established that there is a problem, the conservator can determine the appropriate solution. New materials are now tested in the laboratory before being approved for use within the Museum. In small areas, control is achieved using specially designed 'scavengers', which chemically absorb pollutants. Some showcase fabrics are interlined with charcoal cloth, an effective pollution absorbent, or with mountboard that incorporates charcoal.
Insect infestation monitoring
to monitor insect
levels in buildings.
Museum collections are susceptible to insect damage. Insects can enter the Museum on visitors' clothes, through open doors and windows, and may be introduced by birds roosting or nesting on the building. The worst enemies of Museum objects include:
- woodworm (Anobium punctatum): eats wood and paper
- carpet beetle (Anthrenus verbasci): feeds on feathers, leather, woollen textiles etc.
- clothes moth(Tineola bisselliella): eats textiles
- silverfish (Lepisma saccharina): grazes on paper, starch and dust
The presence of insects in the Museum can be monitored using 'blunder traps'. The traps are placed at likely points of entry and at vulnerable sites and any insects that walk across them will be trapped in the non-setting glue. If pests are found, appropriate measures can be taken.
Museum objects are fragile and need to be handled with great care. Before moving objects the conservator will ensure that the route to be taken is free of hazards and obstacles (is the doorway wide enough?), that the object is properly supported at all times during the move, and that there is a safe place to put it afterwards. When carrying a pot, for example, the base must be supported using both hands and never lifted by the handle or rim. Equally a framed painting should be carried with the bottom edge and both side members supported, and not held by the top edge only.
You may have seen notices around the Museum asking you not to touch the sculpture. This is to prevent contamination from the natural oils present on your hands. If you have ever watched a surface being dusted for fingerprints, you will realise just how much residue is left behind by the cleanest of hands. When the collections are handled, gloves should be worn.
tissue padding, and a polystyrene
crystal box with inert foam padding.
Until recently little consideration was given to the importance of storage methods and materials, often with the result that further damage was done to the objects. It is now recognized that proper attention to storage plays a major part in an efficient conservation programme. The conservators at the Ashmolean are gradually replacing unsuitable materials, ensuring that those used now are of archival quality, free from pollutants. Tissue paper, mountboard and cardboard boxes must be acid-free; polystyrene crystal boxes and polyester films must be inert; and the various grades of synthetic wadding and foam used to support delicate items are tested and approved for Museum use. A systematic programme to replace wooden storage units with metal ones is being implemented.
Treatment when needed
Conservation treatments are no longer carried out as a matter of course, but only in those cases where the conservator considers intervention is necessary for the stability of an item. 'Necessity' can often be a consequence of earlier treatments that have not withstood the test of time and have broken down, damaging the object. A good example is that of an adhesive which has become brittle, discoloured or shrunk.
The conservator will always choose to keep any intervention to a minimum level, carrying out research to find the most suitable and least aggressive method. Every stage of the treatment is fully recorded and documented and after the object is returned to display or storage its condition will continue to be assessed.
Cleaning with laser radiation is a conservation technique increasingly used for removing dirt from the surfaces of many objects made of organic as well as inorganic materials (such as marble, terracotta, painted wood, ivory, paper or leather).
Laser (an acronym for Light Amplification by Stimulated Emission of Radiation) is energy in the form of extremely intense light emitted in a highly collinated beam - this means that the beam is very focused, it does not lose light out to the sides as is typical of other light sources. Such energy breaks the bond between surface dirt and an object and consequently removes the dirt. However, this technique works better on some materials than others and is heavily influenced by the wavelength, pulse length and energy density used. Lasers are also used for other purposes such as 3D scanning.