CRITERIA FOR TREATMENT OF COLLECTIONS HOUSED IN HISTORIC STRUCTURES
3 THE CHALLENGES OF ENVIRONMENTAL CONTROL
The exhibition of collections in historic houses rather than in art museums also affects the structural component of conservation treatments, that is, activities designed to strengthen objects and prolong their lives. The trend in museum conservation has been toward less intensive individual treatment. This trend relates directly to increased emphasis on environmental control. If museum galleries can be maintained at stable relative humidities year-round, then canvas paintings, panel paintings, bronzes, and other materials susceptible to damage or deterioration from unstable or inappropriate relative humidity levels can be maintained with less intrusive treatment than would be needed in less desirable environments, particularly if a conservator is available to check on condition periodically and carry out minor treatments when necessary.
3.1 RELATIVE HUMIDITY AND LIGHT
Even though improved environments are increasingly emphasized in historic house museums, many unalterable facts will make it impossible to provide ideal RH levels in these settings. In art museums without gallery-wide RH controls, RH-sensitive objects can be displayed in tightly sealed cases or frames that either actively or passively control RH changes. In period settings, neither approach is likely to be appropriate. Unstable ambient relative humidities may be an understatement, since, aside from seasonal and diurnal variations, the buffering capacity of the house as a container may be compromised by open doors and windows. Gusts of outdoor air blow into houses every time the door opens. Although temperature levels in museums may not be ideal, they are usually quite steady. Many historic houses are unheated during the winter; heating may be turned on for a few days several times during the season, creating RH changes of a magnitude that would almost never occur in a museum.
It should be unnecessary to mention the role of light in deterioration and the difficulty of controlling natural light from windows and skylights to standards accepted in museums. For all the discussion of ultraviolet filters, visible filtration, window treatments, and plantings to bring light levels down, few historic houses are likely to have the lighting controls commonplace in art museums.
3.2 ROUTINE MAINTENANCE
Light and relative humidity may be the most significant hazards in museums, but environmental protection of collections in historic houses may involve other hazards, including visitors touching objects or brushing against them. Routine cleaning and maintenance procedures also create problems. Several years ago, we performed a survey in a historic house museum where many of the small objects sitting on furniture had chips around the bottoms. The staff told us that the furniture was dusted every day and that each object was picked up during this process. We suggested that dusting be reduced to once per week. Frequent vacuuming or sweeping has similar and all-too-familiar effects on the aprons and legs of furniture. Objects in a historic house may in fact be subjected to routines closer to those of a well-run household than of a museum, with frequent vacuuming, dusting, and polishing of metals and furniture finishes. This work needs to be supervised closely to strike the optimal balance between neglect and overhandling. Conservators need to be aware that any measures that reduce the need for housekeeping will protect collections while also saving staff time and expense.
3.3 OTHER HAZARDS
The wearing of original period costumes has become less frequent in historic houses, but it is not uncommon for original fireplaces to be used for cooking demonstrations. Even if original furniture is not used for its original purposes, floors, doors, and windows have functions that continue. Other hazards that are common in historic houses, such as the influx of flies and bees, are problems unknown in most art museums.