Strategies for Environmental Control
Relative Humidity and Temperature
An environmental management strategy can be defined as a framework for preserving collections by maintaining continuous and stable housing conditions. This strategy can only be effective if it reflects the realities, the opportunities, and the constraints to be faced when trying to fulfil a collections care role. The constraints are often most easily to defined, and may include:
• the physical limitations of buildings;
• finite resources;
• the perceived need to achieve an "ideal" standard of environment control.
Also, when establishing environmental control, there is often a great difference between a theoretical ideal and what can realistically be attained. This situation can create misunderstanding if impossibly high standards are set. In promoting the need for environmental control, two factors must be emphasized:
• Environmental control is good practice: inhospitable conditions accelerate the rate of decay of materials. Early action taken to control the environment can reduce the rate of deterioration.
• Environmental control enables custodians to bid more convincingly for financial assistance from public and independent sponsors: demonstrating a track record of care can persuade sponsors that money is worth investing in an organization.
Once a need for improvements has been established, a decision should be made on the most suitable approach to achieve and sustain environmental control. There are a number of options from which to choose, all of which will require a cost/benefit appraisal:
• whether to move the instrument or collection to another location;
• whether improvements can be carried out on the current site;
• whether to attempt building-wide, or localized control;
• whether to opt for active or passive control.
Active control involves the use of machinery to maintain chosen levels, while passive control relies upon natural responses of the building and the artifacts. Many musical instruments are composite objects, containing a wide range of sometimes incompatible materials. They have often been preserved in uncontrolled conditions for many years, in spite of their mixture of environmentally sensitive and physically robust materials. However, it must be understood that the kind of uncontrolled conditions encountered in a solid, well-built historic house will be dramatically different from those of an out-building or attic. A conservation assessment should indicate if objects kept in such conditions have been exposed to passive environmental control, and whether maintaining the status quo would be more practical than using an active, mechanical system with its drawbacks of reliability.
The level of funding will dictate how the strategy can be put into practice:
• Collections with ample funding might concentrate on incorporating as many passive design features as possible within a building, and choose construction materials that can buffer the effect of the weather.
• Collections with adequate funding might concentrate on localized, zonal, or microenvironmental control around the instruments, using passive means where possible.
• Collections with little or no money should work at the staff level to improve the management of existing resources (time, money, equipment, staff, etc.) in order to maximize their effectiveness at controlling the environment.
Given the reality of limited resources, a strategy should be developed that will deliver the greatest conservation cost/benefits, and that will meet the needs of the most vulnerable objects in the collection. In recent years, the growing acceptance that environmental control may be achieved by different means has led to a thoughtful reappraisal and questioning of the need for strict mechanical control of relative humidity and temperature.
In historic houses it has been difficult to balance the sensitivity of the fabric of the building with that of the contents. A widening of the relative humidity range to something appropriate to local conditions has been found acceptable, because tighter control risks damage to the building. This relaxation has in most cases not affected the contents. This is not to suggest that it is now acceptable to digress from "tight" control in every circumstance, and in the case of functioning keyboard instruments tighter control is certainly warranted. Decisions should be based on an understanding of collection care needs. For example, the vulnerability of instruments to relative humidity fluctuations should be established by studying their method of construction and amount of degradation before deciding on a wider control range.
It may be found unnecessary to spend money on equipment to control relative humidity to +/-2% when the benefit to objects is almost indistinguishable from +/-5% or higher. Relaxation of norms has some important