«Te Papa National Services He Rauemi Resource Guides Preventive Conservation Collection Care Preventive Conservation How do you safeguard the items in ...»
Te Papa National Services
He Rauemi Resource Guides
Collection Care Preventive Conservation
How do you safeguard the items in your museum? This
resource guide looks at practical steps you can take to ensure
the protection, safety and security of your collection.
What is preventive conservation?
Preventive conservation is the practice of safeguarding the items you have in your care.
It begins the moment you accept an object into your collection. It is achieved by
• effective control of your building’s environment 2 Planning for
• safe handling and display techniques emergencies
• good storage 3 Risks and preventive actions
• pest management
• effective security
• planning for emergencies.
Looking at your museum through a preventive conservation lens will reduce the likelihood of damage and decay and avoid unnecessary, and often costly, remedial treatment or loss of valuable items.
Self help in preventive conservation This guide aims in particular to help those museums that don’t have ready access to specialist conservators. It identifies common risks to collections and suggests actions you can take to prevent risks from becoming realities.
Even if resources are limited, there is much you can do to maintain museum collections in a stable condition through applying the principles of preventive conservation outlined in this guide.
When deciding on actions, though, remember that it is necessary to consider the whole situation. Threats to a collection are numerous and rarely exist in isolation. For this reason, it is not possible to cover them all in detail in a publication of this kind.
JUNE 2001 ISSN 1175-6462 ISSUE NO.5 Planning for emergencies Priorities in preventive conservation Emergencies threaten collections. All museums need a plan of actions to be taken should some possible emergency occur in the future. A contingency plan covers this. It sets out what you will do in the event of an emergency - how you will handle it and how you will recover from it.
Contingency plans are often the last thing that people want to think about. In fact they should be one of the first things covered if you are taking preventive conservation seriously.
For an overall picture of preventive conservation, you should read this guide in
• Minimising Disaster (Te Papa National Services Resource Guides 6) which looks at planning for handling and recovering from emergencies
• Emergency Procedures (Te Papa National Services Resource Guides 7) which looks at developing plans and procedures for immediate response to emergencies.
PLANNING FOR CONTINGENCIES OFTEN REVEALS WEAK POINTS
IN YOUR RESOURCES FOR SAFEGUARDING YOUR COLLECTION.
Highlighting problems When you undertake a contingency plan, you may identify problems that need expert attention or would be very costly to remedy. If you understand the principal causes of deterioration in collections, you can still protect them from unnecessary damage. You can take preventive measures that stabilise conditions until a specialist can deal with the situation or you can afford a better solution.
If resources are limited for a long-term solution, your understanding of preventive conservation may help you to think creatively about an acceptable alternative.
Suggested actions for problems Higher budget
• If you see major problems, get professional advice from a conservation architect or building specialist. Ask for a thorough survey of the building and recommendations for improvements on areas of concern.
• Prioritise the repairs you need and get quotes from tradespeople to determine the potential cost of repairs. Apply for funding.
• Do whatever maintenance you can to reduce the risk to collections. For example, make sure the property is regularly inspected and maintained, clear rubbish regularly, prune trees, improve security lighting to discourage vandalism when the museum is closed.
The initial reason for preventive maintenance of this kind may be the care of collections, but other benefits are improved building maintenance, less damage to collections through pollution, dust, dirt and moisture, and a better environment for museum staff and visitors.
The environment inside the building
Relative humidity Relative humidity (RH) is a measure of how much water is in the air compared with how much there would be if it were fully saturated at the same temperature. RH is shown as a percentage. Damage can be caused by sudden changes in RH or by inappropriate RH for the object. High relative humidity (over 65%) may cause mould and tarnishing. Low relative humidity (under 45%) may cause drying, warping and cracking.
A stable environment in the middle range of 50-55% is considered the best compromise and is the accepted standard to aim for. Without a climate control system or only minimal control a range of 45-60% is acceptable, but large, sudden changes should be avoided if possible. Gradual or seasonal fluctuation can be allowed for within this range.
Relative humidity and temperature can be easily measured using a wet and dry bulb psychrometer. This will give an ‘on the spot’ reading. However, it is better to record environmental changes over time using a datalogger or thermohygrograph. These instruments will show changes that occur over a weekly or monthly period and provide more information on climatic changes.
More on relative humidity To explain relative humidity very simply: when RH is at 50%, the air is holding half the water it could at that temperature (the warmer the temperature, the more water the air can hold). A reading of 30% RH means the air is very dry, a reading of 95% RH means it is almost saturated.
The type of damage high or low levels of humidity can cause depends on whether the object is organic or inorganic. If it is organic, for example, paper, wood or textiles, fluctuations in RH will cause swelling and contraction that may stretch, crack or tear an object. If the object is made of inorganic materials, such as metal, moist conditions will cause corrosion and swelling of the products of corrosion. Some inorganic materials such as ceramics, glass or gold are much more durable, and will be less affected by moisture.
High RH may also encourage the growth of moulds. Mould will stain and eat away organic materials.
Measuring Relative Humidity A thermohygrograph (left) has the advantage of being clockwork-driven and easily maintained. You will need a wet and dry bulb psychrometer to calibrate it. A new thermohygrograph costs about $1400 but you can sometimes find them in second-hand equipment shops or surplus to requirements at engineers’ offices.
A wet and dry bulb psychrometer (right) is a battery-driven instrument and you have to dampen the wet bulb to get a reading. It costs about $800 new.
A datalogger (centre foreground) costs about $450 new and you’ll probably need to renew it every 3-4 years. You need suitable computer equipment to access its data, and calibration, if needed, can be expensive.
Temperature Temperature can affect collections in similar ways to humidity as the two are closely related. A rise in temperature in your building will reduce RH while a drop in temperature will increase it.
If you had limitless resources, it would be better to provide two ranges of temperature in your museum: lower temperatures for collections and higher temperatures for staff and visitor comfort. For example, the environment for collections could be within the range 15-18 °C (in some cases very much lower than this); another environment for staff comfort within work areas could be within the range 20-22 °C. This requires more than one building system and is extremely costly.
For practical reasons, and where cost is a consideration, the best temperature for both collections and human comfort is a range of 18-22 °C.
Any changes in temperature need to be gradual and controlled.
Air cleanliness There are three main sources of pollution from the air - gases, particles (for example, carbon from vehicle exhausts) and fungi.
• Paint, adhesives, building materials, plastics and wood, give off gases that cause corrosion and decay of museum objects. An example might be frequent tarnishing of metal objects made from silver or copper.
• Particles in smoke, dust lint and pollen cause abrasion.
• Fungi may cause mould when conditions are moist.
A filtered climate control system will help reduce pollutants or keep them under control, but this may be too expensive for many museums.
Suggested action for problems Higher budget
• Get professional advice from a heating and ventilating engineer.
• Ask a conservator to undertake a survey of environmental conditions and to provide a written report.
• Try increasing control of the environment by sealing doors and windows to reduce draughts.
• Use appropriate measuring instruments to monitor and record conditions. Ask a mechanical engineer at your local council or a preventive conservator for help in acquiring and using the instruments mentioned above.
• Pack special items in crates or boxes for protection. This will slow the effect of environmental changes by creating a microenvironment within the container and help buffer contents from external changes. Seal wooden surfaces to reduce gas being given off from them.
HEPA filters The HEPA (High Efficiency Particulate Air) filter is made to a recommended international standard that requires its efficiency to retain particles as small as 0.3 microns and has an efficiency rating of 99.97%. The filter was developed by the Atomic Energy Commission to remove radioactive dust from atomic plant exhausts.
• Air cleanliness can be improved by regular vacuum cleaning - this will help reduce dust particles. Ensure the cleaner has a good filter system to prevent dust blowing back into the air through the cleaner exhaust. A cleaner fitted with a HEPA filter is the most efficient.
Natural light and artificial lighting There are three main causes of damage from natural light: ultra-violet radiation (UV) (measured in microwatts/lumen); visible light (measured in lux); and infra-red radiation causing heat damage.
UV radiation must be kept below 75 micro watts/lumen. There are many products available that filter UV, including films, filters and low UV lamps. They are readily available from lighting, glass and window specialists and easy to install.
Visible light is measured using a lux meter. Visible light should be kept within the range of 50 lux or lower for very sensitive objects such as watercolours and textiles, and 150lux for less sensitive objects, for example, oil paintings.
When you have information on light levels it is easier to make the right decisions to rectify potential hazards.
Dangers from daylight Many smaller museums are in buildings previously used as family residences. These do not have filtered windows and use a lot of natural light to display the museum in the way it may have appeared to its occupants. This is unfortunate because natural light is causing irreversible damage to furnishings and items on display. On a sunny summer day, light levels can be as high as 50,000 lux just inside an unfiltered window.
Suggested action for problems Higher budget
• Consult a lighting expert, describe your requirements and ask how these can be achieved.
• Ask a conservator to measure light levels with a UV and lux meter and write a report on the conditions. Alternatively, ask an electrician, they sometimes use lux meters in their work.
Humidifiers and dehumidifiers A common problem in winter is office air conditioning without humidity control. The air outside is cold and dry, and when it is drawn into a building and warmed, more moisture is removed. This can create a very dry environment sometimes as low as RH 30%. This causes cracking, warping and splitting of organic materials, for example, wooden furniture.
If this is a problem, a humidifier will help increase moisture and thereby reduce the drying effect. In cases where too much moisture is present a dehumidifier will remove excess moisture. Monitoring equipment will be needed to determine exact levels of moisture in the air.
• Use curtains or blinds which can be closed on bright sunny days. Avoid placing objects close to unfiltered windows
• Reduce natural light. Keep artificial lighting to recommended levels.
Storage and handling For many museums, lack of space is usually the biggest problem for managing safe storage and handling. This can sometimes be overcome by reorganizing collections and using available space differently.
Lack of use is another common problem. Often storage rooms are left untouched for years allowing the effects of dust, dirt, insect infestation, moisture and mould to accumulate unnoticed.
Long-term exhibitions can have similar risks for objects on display as storage.
Suggested action for problems Higher budget
• Improve storage conditions, including more space, new shelving, open crating systems, improved cataloguing and recording procedures. Perhaps consider some off-site storage.
• Survey collections or do a feasibility study to determine collection needs. Apply for a grant to cover costs. The survey will provide vital information for decision-making on storage improvements.
• Attend training on storage and handling to gain a better understanding of issues and solutions.
• Use water-based polyurethane to coat or seal surfaces on wooden shelving to reduce the amount of gas the wood gives off.
• Fit restrainers to objects to prevent damage (and possibly injury to people) from their toppling or falling off shelves.
• Create a small work area to provide space for working on collections.
• Wear gloves when handling objects to reduce tarnishing and transferring dirt from one object to another.