Appropriate Design Solutions
Multilevel Conservation Response
- Design for stability and protection. Choose an appropriate and efficient response from among the multiple options available. Consider what level of protection is obtainable and what kinds of tradeoffs each will impose on the conservation criteria. Factors include environmental and structural stability, both catastrophic and cumulative risks.
- Consider both macro and micro approaches. Weigh the benefits and costs of addressing conservation criteria throughout the exhibition against creating micro solutions using exhibit cases.
Conservation criteria are realized through thoughtful exhibition design. Experience and research have consistently shown that the design of the overall exhibit space (the macroenvironment) and the exhibit cabinetry (the microenvironment) affects the long-term condition of objects. Preservation-responsible exhibition design need not be an all-or-nothing proposition. Conservation criteria can be met using a variety of design options. By selecting the appropriate level of conservation response, the exhibit design can be tailored to specific object requirements.
Preservation-responsible design involves conscious choices and tradeoffs. Not all objects require the same level of conservation concern. Some exhibits require no special precautions, while others mandate very stringent measures. Working together, the designer and conservator consider how different design options will affect the objects and their needs. The curator and the team member administering the budget often help decide on the final, balanced approach.
The principal difference between macro and micro strategies is the size and scope of the conservation features required. Managing the environment throughout the building or exhibit space is ideal, because all exhibit elements and collections will be under identical conditions. In many institutions, however, this approach proves unrealistic, unfeasible, or not cost-efficient. A smaller-scale, more self-contained approach satisfies the conservation criteria locally. The goal is to separate the vulnerable objects from the sources of deterioration and control the immediate surroundings of the objects on display.
Most successful exhibitions employ both macro and micro strategies, letting practicality and financial requirements guide design. These exhibits strive for a balanced approach that does not require excessive staff time or maintenance over the life of the exhibit. A main goal common to both strategies is attaining appropriate environmental and physical protection. Exhibit design should account for down times when the well-engineered feature or system fails and the impact on collections must be carefully considered. Calculate the risks for various design options; establish how long the exhibit can exist under a major failure and project the outcomes in terms of collection safety. Build in safeguards and redundant protection when necessary.
Examine and compare the design options. A discussion about climate control, for example, might differentiate between two strategies:
- Macroclimate solution - Start by understanding the nature and capability of your building environment (including climate, light, and pollutants) and how it matches your general and specific object needs. Also critical, is understanding your seasonal outdoor environmental conditions and assessing your environmental data. If you are using an active environmental system, understand potential for failure and plan for these situations. The temperature and humidity in the entire exhibit space can be controlled with the building's mechanical system, either by adjusting existing equipment or by installing additional room-specific HVAC and humidifier units. This approach provides optimum protection for all objects, but it is not always practical. The disadvantages include the expense of installation, operation, and service; the difficulty of installing new duct work and piping; and the potential for damage to buildings in winter when elevated humidity levels are maintained.
- Microclimate solution - When tight control of the entire macroclimate is impractical for financial or technological reasons, or when only a few of the objects require a more stringent environment, creating a microclimate within an exhibit case is a useful design tool. Because microclimates cannot be created in traditional museum casework, a specially designed, well-sealed, climate-controlled case must be constructed. This approach involves higher cost; longer design and construction time; tighter adherence to design specifications; and stricter exclusion of certain hazardous construction materials. Note that inadequate or incompatible choice of construction materials can be a source of pollution inside a contained environment, particularly for materials that are at risk for deterioration when exposed to these byproducts.
(See Section on Exhibit Case Design, for more information about creating microclimates.)
Exhibit Format and Layout
- Use enclosed display when possible. Avoid open display except in historic house museums and some gallery settings or when an object's size makes enclosure impractical. Open display should never be a routine exhibition option or one chosen solely for financial reasons.
- Allow sufficient room for traffic flow. Design the exhibit to avoid accidents. Provide adequate space through the exhibit and around exhibit cases for the easy movement of individuals, groups, and people in wheelchairs.
- Group similar objects. Consolidating the location of collections with similar conservation criteria will make it easier and less expensive to meet the design goals.
Open or Enclosed Display?
Any group of objects displayed without protective enclosures can be defined as an open exhibit. Given the inherent problems for collections care and preservation, open display is rare for long-term museum exhibits, except those in historic buildings and sculpture or painting galleries. Usually, open displays are limited to temporary exhibits and the display of reproductions or oversized artifacts. The ultimate decision to display objects outside protective enclosures must consider the following variables:
- length of the proposed exhibit
- sensitivity and condition of the proposed objects
- environmental conditions of the exhibit space
- likelihood of visitor contact with or handling of objects
- likelihood of vandalism and theft
- availability of curatorial maintenance resources
Open display requires special security arrangements and regularly scheduled maintenance procedures, which involve long-term, frequently ignored costs. An added problem in such displays is the importance of limiting dust infiltration and moderating the environmental conditions in the entire exhibition area.
Although display in cases is the norm for most museum exhibits, the benefits of enclosure are rarely calculated methodically. If designed appropriately, an exhibit case can protect its contents from most forms of physical damage and deterioration. An exhibit case can be designed to:
- prevent object handling and incidental touching;
- decrease the threat of theft and vandalism;
- stop insect and rodent access;
- block out dust and foreign substances;
- buffer collections from rapid changes in temperature and relative humidity;
- remove or limit harmful light radiation; and
- allow for the use of environment modifying agent
(such as absorbers for atmospheric pollutants, moisture responsive substances, and oxygen scavengers).
Pathways through the exhibit and around freestanding casework must allow unrestricted, safe movement of people and wheelchairs. Americans with Disabilities Act (ADA) standards call for a minimum of 36 inches for any walkway and a 60-inch diameter for turns. Cases or other display components that protrude from a wall should allow a 27-inch clearance from the floor.
A well-designed floor plan also allows for human behavior. For example, a freestanding case should not be placed where it is likely to be bumped. A fragile object is at risk if visitors can touch or brush against it, if its display pedestal or case can be rocked or moved, or if it is not mounted securely to prevent falling over. The educational programs associated with many exhibits require an area where schoolchildren and tour groups can gather. Such spaces should be located away from areas of heavy object density.
While interpretive and practical considerations are the primary criteria when designing the exhibition layout, creative, thoughtful design can alleviate conservation- related difficulties within the exhibit space. For example, blocking windows can allow safe display of light-sensitive objects. Grouping objects that have similar humidity requirements within the same case means that a micro- climate display case is both practical and cost-effective. Likewise, grouping light-sensitive objects gives the designer more flexibility in the exhibit lighting plan.
The presentation of displayed objects involves overlapping design and conservation strategies. Thoughtful arrangement of objects inside a case facilitates their installation, periodic maintenance, rotation and emergency removal.
Objects that must be displayed in the open, especially oversized objects, require sufficient space and specialized mounts to prevent accidental damage. However, the need for barriers increases the overall space required for the safe exhibit of these pieces. On the other hand, a high-security exhibit case protects its valuable contents from theft but strongly influences the interpretive and aesthetic options.
Understanding the Exhibit Environment
Temperature and Relative Humidity
- Know the environment. Monitor an exhibit space for one year to obtain baseline information about the temperature and relative humidity. Review these environmental data for each exhibit to determine if existing conditions meet the conservation criteria.
- Control the environment within the entire exhibit space. In general, keep temperature between 60 and 70°F (15.5 and 21°C) and relative humidity between 40 and 60%, eliminating rapid cycling of temperature and relative humidity. Requirements for special objects and certain geographical areas may vary.
- Locate sensitive objects in the most stable locations. Do not place moisture-sensitive collections in the path of direct sunlight, near heating or air-conducting ducts, against external walls, or in damp locations such as basements. Avoid putting cases and framed works along exterior walls.
- Provide additional control for sensitive objects. When appropriate use sealed cases to slow air exchange and thus stabilize environments inside cases. Consider creating a microclimate by incorporating silica gel or other climate control products within cases that contain moisture-sensitive materials.
Conservation criteria for temperature and relative humidity are often necessary because of the range and severity of physical, chemical, and biological damage caused by exposure to excessive or rapid cycles in temperature and humidity. Organic materials are sensitive to temperature and relative humidity levels. Inorganic materials, on the other hand, are usually unaffected by moderate cycles.
Temperature affects the rate of most chemical deterioration processes, which double for every increase of 18°F (10°C). Some materials, such as plastics, photographic emulsions and rubber-based materials, become soft or tacky at higher temperatures. Other materials become more brittle and are easily damaged by handling or physical stress at low temperatures. In general, temperatures in the exhibit area should be kept below 80°F (26.6°C), even in hot climates, and above 32°F (0°C). Dramatic and rapid changes in temperature must be checked to prevent thermal shock to glass, enamels, and some other inorganic materials.
An acceptable range of relative humidity for many parts of the country is generally 40-60% RH, with a winter low of 35% in colder, northern climates. In areas that experience dryer ambient climates, such as the Southwest, a lower humidity range (30-40%) is appropriate. In tropical climates, museum collections have been safely displayed in atmospheres approaching 75% RH if adequate ventilation is provided. In addition, objects tend to adjust to (reach equilibrium with) the environmental conditions from which they originate and to those which they are continually exposed.
Whatever the ambient environment of a region, the primary goal is to maintain as stable a relative humidity as possible. Therefore, the rate of daily RH change and fluctuation should not be excessive: ideally 3% but no more than a total of 5% per day. Seasonal change in relative humidity should also occur with very gradual transition. Moreover, it is important to note that some materials are very humidity sensitive (for example, ivory teeth and some minerals) and must be maintained under stricter environmental ranges.
Some understanding of the general climatic patterns in the museum's geographic region can be gained from annual summaries available from the National Oceanic and Atmospheric Administration. A real understanding of the exhibit environment, however, can only be gained by monitoring the conditions in the exhibit space for one year to establish a baseline. If such monitoring is not feasible, projecting or estimating the climatic conditions in the exhibit space may be possible. Evaluation of the climatic records:
- allow the environmental conditions of an exhibit space to be considered when choosing objects for display;
- enable staff to modify existing heating and air-conditioning systems or choose equipment that allows a more optimal range of temperature and RH.
- facilitate the location of more sensitive collections in areas with the most stable conditions;
- point out the need for additional measures, such as providing a microclimatically controlled environment; and
- guide the technical requirements for exhibit case seals.
The concept of a box within a box is a useful one when considering environmental control. The building itself is the outer box, while the exhibit room creates a second zone. The exhibit case further defines the environment around an object. Controlling the environment at these different levels, or at different levels within each "box" is a cost-effective strategy that is appropriate for certain exhibit situations.
The initial selection of an exhibit location should consider the recommended environmental criteria for the exhibit. Making the exhibit area as self-contained as possible helps to stabilize the environment. To encourage a more constant environment, block unnecessary windows and doors with insulating material; enclose the exhibit area with well-fitting doors; and provide unrestricted airflow for the heating and air-conditioning systems. Ideally, an exhibition space should have these features:
- no door or windows opening directly outdoors
- few exterior walls
- weather seals and insulated walls, floor, and ceiling
- vapor barriers in the walls, floor, and ceiling
The options for environmental control begin with the overall exhibit space. Climate control throughout the area provides protection for all the objects on display. Macro control is appropriate when most or all of the objects are sensitive to temperature or humidity. In other situations, the susceptibility of the objects, the available human and financial resources, and the schedule will influence the degree of control that is practical.
Improving conditions within an entire area does not always mean adding expensive equipment. Low-cost options include:
- setting the temperature at a level appropriate for the geographic region (in the Northeast, Northwest, and upper Midwest, maintaining a lower temperature in winter will help prevent excessively low relative humidity);
- maintaining temperature set points at constant levels on a 24-hour basis, not lowering temperatures at night;
- controlling the heating and air-conditioning (HVAC) system with a humidistat rather than a thermostat; and
- using portable dehumidifiers during problem periods, such as the last weeks of summer when visitation is traditionally high.
Object location is important when designing the exhibit layout. Place humidity-sensitive objects away from sources of humidity fluctuation, including exterior door- ways, windows, air vents, artificial and natural light and heat sources, and exposed pipes; do not place objects in damp basements. To prevent damage from desiccation and dimensional change, avoid overheating objects resulting from displaying them too close to a lighting source or allowing heat from lights or transformers to build up inside an exhibit case.
The choice and placement of light fixtures can cause thermal change and therefore influence relative humidity and the moisture content of objects on display. Inappropriate exhibition lighting heats up the objects. More than 90% of the energy from an incandescent lamp is heat, and every watt of light adds 4.15 BTUs (British thermal units) to the heat load of the building. Some exhibitions incur air-conditioning expenses year-round as a result of the heat produced by poorly designed lighting systems.
When the overall climate conditions in the exhibit do not meet the conservation criteria for humidity-sensitive objects, a tightly sealed exhibit case can offer the required protection. By decreasing the rate of air exchange, sealed cases buffer the objects from the worst ambient humidity swings. The use of silica gel can stabilize the humidity level within a sealed case in exhibit spaces with little or no humidity control.
To prevent the transfer of exterior temperatures from affecting the internal temperature and humidity of exhibit cases, cases should not touch a building's outside walls. Similarly, framed works should not be hung on external walls. When the location of a case or frame cannot be changed, consider the use of insulating construction materials and thermal pane glass.
- Monitor pollutants and enclose sensitive objects. Incorporate air filters in ventilated case designs or seal exhibit enclosures sufficiently to prevent particulate entry. (see TechNotes Monitoring Pollutants Inside an Exhibit Case)
- Use high-efficiency filters. HVAC equipment should remove particles down to 1-0.3 microns (60-80%). Change filters regularly.
- Use localized filtration equipment as needed. If improving filtration throughout the museum is not feasible, consider using room-sized units in construction areas or within the exhibit space.
An accumulation of dust can obscure or stain an object's surface, reducing its visual impact or interpretive usefulness. Oily and sooty deposits, in particular, may be impossible to remove from porous or fragile surfaces. Particulate matter ranges in size from visible to microscopic.
Particulate pollution is drawn into a building through natural ventilation and the environmental control systems. Particulate matter (dust in the air around us) is a complex mixture of airborne soil, carbon soot, textile fibers, microorganisms, and protein materials. This combination can be abrasive, attract moisture, and encourage insects, fungi, and mold.
The ambient air quality will depend on local pollution sources and wind direction. Data about the amounts of particulate matter in the ambient air of many cities can be obtained from the U.S. Environmental Protection Agency and regional weather and air quality control stations. In addition, dust generated in the museum will add to the ambient particulate matter.
Various methods of reducing particulate pollution in exhibits are available. Limit the infiltration of unfiltered air through cracks and gaps in the building by caulking or gasketing doors and windows. Keep windows closed. Incorporate a vestibule at the exhibit entrance to control airflow. Use grates to capture dirt from visitors' shoes. Creating a positive room pressure through adjustments of the air handling system will further limit the influx of potentially polluted external air.
Control particulate matter through a combination of macro and micro solutions, including enclosing sensitive objects and providing adequate filtration.
No matter what the ambient level of particulate pollution, any museum collection should be protected from gross amounts of dust. Protection can be provided at a variety of levels, depending on the severity of the pollution problem and the sensitivity of the collections. At a minimum, filter the air entering the museum's heating and cooling systems to remove particulate matter larger than 1 micron.
|Particulate Matter||Particle Size (in microns)||Filter Efficiency|
|Soil dust||100 - 1|
|Coal dust||100 - 1|
|Household dust||5 - .01||Panel filters (10)|
|Insecticide dust||9 - 1|
|Tobacco smoke||5 - .01||Media filters (.5)|
|Carbon particulate||1 - .001||HEPA filters (.01)|
Particulate Pollutants and Filtration
Dust and lint filters used in residential systems, also called panel filters, are generally not effective enough for museum applications because, at best, they only remove particulate matter larger than about 10 microns. Media air filters, which are often pleated to increase surface area and to help limit the subsequent drop in air pressure, are more efficient and can remove up to 35% of particles larger than .5 microns. The most effective HEPA (high-efficiency particulate-arresting) filters provide more than 99% efficiency for particulate matter as small as .01 microns. As long as the equipment can operate under lower air pressures, replacing panel filters with media or HEPA filters provides a dramatic improvement in air quality.
Keep HVAC systems well-maintained, and clean humidifiers, cooling coils, and drains regularly. To prevent salt and mineral deposits from hard water (also called white dust accretions) from settling on museum collections, supply ultrasonic humidifiers with distilled water.
Reducing the amount of air taken in from outdoors can improve the efficiency of the filtration, although the system must be operated within the minimum requirements set by the American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE). Visitor traffic and necessary staff functions, including exhibit construction, create particulate matter; recirculated air must also be filtered.
If cost or practicality prohibit filtration of the entire museum building, room-sized air cleaners are very effective when used in a confined space such as an exhibit preparation area, an exhibit space during construction, or a finished exhibit. Some commercial units remove more than 99% of particulate down to a size of 0.3 microns; many also incorporate an activated carbon prefilter that removes gaseous pollutants.
When objects on display are particularly susceptible to damage from dust buildup, the optimum level of protection is provided by enclosing them inside a case. A sealed exhibit case restricts airflow so that particulates are not drawn into the exhibit case. Air movement through a ventilated case must be filtered to remove particulate matter.
- Monitor pollutants. Assess the air quality within the museum to establish the ambient level of contaminates. This knowledge will point to the measures necessary to meet the conservation criteria for an exhibit. (see TechNotes Monitoring Pollutants Inside an Exhibit Case)
- Incorporate chemical filters in the environmental systems. For susceptible collections or in highly polluted locations, include activated charcoal or potassium permanganate filters in the environmental system. (see TechNotes Using Pollutant Absorbers Inside and Exhibit Case)
- Provide air circulation. Adequate air circulation will lower total pollutant concentrations; high rates of airflow over or near objects, however, increases their exposure. Design the exhibit layout to minimize the objects' exposure to pollutants.
- Select stable construction materials. Avoid materials known to emit hazardous materials, become acidic, or lose their physical or chemical stability with age. (see: Choosing Materials for Storage, Exhibition & Transport)
- Aerate the exhibition space before object installation. Allow at least 3 weeks for initial levels of outgassing from new materials to dissipate.
- Enclose sensitive collections. Sealed cases that incorporate a chemical pollutant scavenger provide a high level of protection for sensitive objects.
Chemical pollutants in a museum originate from both external and internal sources. Sulfur and nitrogen oxides, hydrogen sulfide, chlorine compounds, and ozone are some potentially harmful chemical pollutants commonly found in the exterior environment. Construction and design materials may emit chemical vapors such as formaldehyde. Both organic materials (such as textiles, paper, and animal skin products) and inorganic materials (such as silver metals, silver-based photographic images, shell, and some minerals) are susceptible to deterioration by corrosive airborne pollutants.
Control of chemical pollutants becomes a very serious conservation concern for materials that are particularly sensitive to low concentrations of gases. These materials include those that are highly vulnerable to acids; metals such as lead, silver, and their alloys; solder; and shell or other materials containing calcium carbonate. Sometimes, well-sealed exhibit cases pose dangers; even a small amount of continuous outgassing can raise chemical concentrations to hazardous levels in confined spaces.
The U.S. Environmental Protection Agency provides information on the concentrations of outdoor pollutants in a city or region. Gaining access to air quality information is helpful because it is the easiest method to identify outdoor pollutants that may be present in an exhibit area. The concentration of chemical pollutants can be measured by quantity (in parts per million or parts per billion) or by weight (such as micrograms per cubic meter). Recommended permissible levels of pollutants within a museum environment vary, but generally they fall below 1 part per billion (ppb).
Because dust attracts and holds pollutants, particulate filtration automatically captures a certain amount of chemical pollution. For this reason, upgrading HVAC filtration in a museum or exhibit space is the first defense against chemical pollutants. For sensitive collections or in areas that are highly polluted, the additional step of incorporating activated charcoal or potassium permanganate filters into the environmental system is often required. Such filters should reduce sulfur and nitrogen dioxides to a level below 10 micrograms per cubic meter of air. Air from areas within the museum known to generate pollutants-including exhibition preparation areas such as spray booths and printing facilities-should be prefiltered or exhausted directly out of the building.
Good air circulation usually reduces the tendency for pollutant concentration to occur. A high rate of unfiltered airflow across the surface of an object is not recommended because it increases the total exposure to potential pollutants. Because elevated temperature and relative humidity accelerate the evolution of chemical pollutants, maintaining a moderate climate is beneficial. Wide fluctuations in relative humidity can cause localized condensation that results in elevated pollution levels and reaction with object surfaces.
The exhibit design and production process can control the exposure of objects to dust and pollutants. As with other conservation issues, the location and placement of objects can be an important design tool for limiting the effects of pollutants. Follow these general guidelines:
- Isolate objects from direct contact with exhibit construction material with a neutral layer or film, fabric, or cushioning foam, or elevate objects with mounts.
- Do not enclose objects inside cases with chemically unstable materials.
- Locate sensitive objects away from doorways, air return ducts, walls that experience a temperature gradient, and other locations that have rapid airflow.
- Provide air space between collections and known pollutant sources (concentrations of pollutants are highest near a contaminant).
- Avoid creating pockets of still air in which pollutant levels can concentrate (for example, long runs of cases that extend from floor to ceiling).
Some objects are particularly sensitive to the chemical processes initiated by airborne pollutants. To provide the highest level of protection, enclose these objects in well- sealed cases or frames that include a chemical absorbent. The option of a ventilated case with filtered vents, as well as a sealed case, is discussed in more detail in the section on Exhibit Case Design.
Choice of Exhibit Construction Materials
Some materials used to construct or decorate exhibit cabinetry have proven to be chemically unstable. Damage can occur when exhibit objects are in direct contact with unsuitable and unstable substances, such as wood, fugitive paints, soluble dyes, and oils. Damage also results from the outgassing of vapors from volatile organic substances, including acids, formaldehyde, and solvents. Many materials contain additives and unspecified chemical reagents. (see: Choosing Materials for Storage, Exhibition & Transport and Exhibit Case Construction Materials)
Outgassing often occurs when a material is new, but it may continue throughout the life of the material, some- times increasing over time. Problematic additives and parent materials include:
- acidity from low-quality mat boards, many paper and wood products, fabrics, paints, and adhesives;
- chemically unstable plastics;
- unreacted monomers and solvents from otherwise stable compounds;
- additives that, over time, migrate out of a plastic and deposit onto the objects; and
- surface finishes such as fire-retardant products in textiles and ultraviolet radiation absorbers in plastics.
When selecting construction and finishing materials, consider their stability. Because manufacturers may change the composition of commercial products, a product used in a previous application may no longer be acceptable. Test each batch of a product before use. Commercial testing services are available, and conservation laboratories can perform some less complex tests. Many materials can be eliminated from consideration before the testing phase.
Base the initial selection of materials on information gathered from:
- results of previously tested and accepted exhibit materials;
- the manufacturer's product literature;
- the safety data sheet (SDS), which lists basic components and safety precautions for the product's use; and
- the manufacturer's technical department.
Problem materials can sometimes be used safely in small quantities in large, open exhibit areas with good air circulation and filtration. Material stability is particularly critical, however, when large quantities of pollutants are used throughout the exhibit space or within a sealed case.
Before objects are installed, all surfaces and construction materials must be absolutely dry and fully cured; paints, adhesives, and caulks generally require a minimum of three weeks to dry. Aerating the overall exhibition space and the exhibit cases before object installation allows some of the highest levels of pollutants to dissipate. Newly painted surfaces should be allowed to cure totally before objects are installed. Heaters can be used to speed the curing process. For highly sensitive collections or after major construction, it may be advisable to purge the entire exhibit or the cases using a portable air filtration unit, which can generally be procured locally.
Sensitive objects can also be enclosed in a ventilated display case that incorporates a pollutant sorbent such as activated charcoal or potassium permanganate. Such a case provides a low risk environment for sensitive collections. Pollutant sorbents also prevent tarnishing of polished metal surfaces.
- Develop a lighting plan that responds to the established conservation criteria. Produce the plan early in the process to allow enough time for coordination of the complex issues that determine final lighting choices and levels.
- Limit total light exposure. Provide separate lighting for security checks, exhibit cleaning and maintenance, object installation, and other routine work. Turn off lights during nonpublic hours so as not to expose objects to light unnecessarily. When possible, use occupancy sensors in the room or at the case to turn lighting on and off during visitation hours.
- Filter all sources of ultraviolet radiation. Use commercially available filters on all light sources to reduce the levels of ultraviolet radiation to 10 microwatts per lumen.
- Control infrared radiation. Locate objects at least 24 inches from fluorescent lights and at least 36 inches from incandescent or tungsten halogen lights.
- Exclude sunlight. Design exhibit spaces to prevent daylight from reaching display objects. Daylight that is already present in the exhibit space should be filtered for UV radiation and lowered in intensity.
- Construct lighting mockups. Evaluate the amount and quality of light provided by the proposed lighting plan. Measure final light levels and adjust them accordingly during installation.
- See: Exhibit Case Lighting
Exposure to light causes irreversible damage to organic materials and some inorganic objects. Types of damage include aesthetic changes (such as fading or shifts in color), as well as breakdown in a material's microscopic structure that results in brittleness and weakness. Three components in light cause damage: visible light, ultraviolet radiation, and infrared radiation.
While general standards for illumination levels exist, the conservation criteria for an exhibit establish specific levels for the preservation of particular objects. Work towards achieving these general footcandle guidelines: (Note:1 footcandle equals 10.764 lux or approximately 10 lux)
- a maximum of 5 footcandles (54 lux) for very light- sensitive materials such as textiles and papers
- a maximum of 10 footcandles (108 lux) for moderately sensitive materials such as unpainted or dyed organic objects and paintings with sensitive pigments or glazes
- a maximum of 15 to 20 footcandles (161-215 lux) for less sensitive objects such as stone, glass, ceramics, and metals
Objects do not "recover" from light exposure; light- induced damage is irreversible and cumulative. An understanding of the relationship between the amount of visible light and the length of exposure is critical for responsible lighting decisions. Both light level and exposure time together determine the degree of light damage.
Note: Footcandles X Hours = Total Exposure
- Example a: 5 fc x 8 hrs = 40 fc/hr exposure
- Example b: 20 fc x 2 hrs = 40 fc/hr exposure
Low illumination levels over a long period are equivalent to high levels over a short period. It is possible, therefore, to illuminate a light-sensitive object at a higher level if the exposure is short and infrequent. There is less flexibility in light levels when an object is displayed for longer periods.
There are many ways to lower the amount of illumination reaching an object. These methods can be used alone or in combination to produce the appropriate amount and quality of light. To ensure that light levels within an exhibit match the conservation criteria, they must be monitored as the objects are being installed. Options for control of visible light include the following:
- inserting diffusers (grids, textured panels, and films) between the light source and the object to redirect and scatter the light
- using rheostatic control dimmers on individual lamps (as opposed to using a dimmer to control several lamps)
- replacing a lamp with a lower-wattage lamp, producing less light
- changing beam aim or width (diameter of the space that a lamp's light beam will illuminate)
- decreasing the number of lamps
- moving the lights farther from the object
Because ultraviolet (UV) radiation is so destructive to materials and because it is unnecessary for seeing the objects, it is standard museum practice to eliminate it from lighting sources. UV radiation is a natural component of sunlight and is also produced by artificial lights, especially fluorescent and halogen lamps.
In the past, 75 microwatts of UV radiation per lumen of light was set as a conservation standard. New products that prevent the passage of UV radiation through window glass, exhibit case and frame glazing, and fluorescent tubes allow the old conservation standard to be super- seded. It is now possible to nearly eliminate UV radiation from any exhibition light source, making 10 microwatts per lumen a practical goal. When objects are displayed in the open, UV filters for individual light sources are needed. For encased objects, common methods include:
- using UV-filtered glazing to construct cases
- glazing frame packages with UV-filtering material
- installing a UV-filtering layer between lights in a case's lighting chamber and the objects
A variety of filters for all lamp types are available to reduce both ultraviolet and infrared radiation. Some fluorescent tubes come coated with a plastic that eliminates UV transmission. Low-voltage bulbs are also available with an integral filter, or they can be filtered with a treated glass. Architectural glass can be filtered with a laminate film, or a special UV-filtering glass can be used instead.
Infrared (IR) radiation is the heat associated with sunlight and incandescent lights. This heat can cause an exponential rise in the rate of object deterioration by speeding chemical reactions and drying out organic materials. Research attributes up to 40% of color loss in dyes to IR radiation. IR radiation can be controlled by:
- using special filtering window glass in architectural elements and case instruction
- applying window films to architectural windows and skylights
- dissipating heat generated from exhibit lights to prevent buildup in confined spaces within, above, or next to exhibit cases or objects
Object sensitivity helps determine the selection of an exhibit lighting system and the development of a lighting plan. To be successful, the lighting plan must take shape early in the design. The impact of lighting in the exhibit and adjacent spaces, including light from architectural features such as windows or skylights, must be factored into the plan. Lighting issues are complex, so the lighting plan should be developed in consultation with the conservator and, when possible, a lighting designer experienced in museum exhibits.
Technical information for the exhibit designer is available from lighting manufacturers, who generally supply reference material and may even provide individual technical advice on the use of their products. In some situations, a lighting designer may be consulted on certain issues or may be responsible for the entire lighting design.
Consider these key issues when designing lighting:
- the available budget
- the future benefit of installing an adaptable lighting system suitable for a variety of installations rather than just one exhibit
- separating circuits and controls for task-specific lighting; controls for security checks, exhibit cleaning and maintenance, and object installation should be separate from controls to illuminate the objects, graphic panels, and other exhibit elements
- developing museum policies and procedures that lower the total light exposure of an object, such as limiting the length of exhibit and lighting display areas only during public hours
- using a room or case occupancy sensor that raises lighting levels only when visitors are present.
Lighting continues to be a conservation concern even after the exhibit opens. Any change in the wattage or color temperature of a bulb or the aim of a lamp alters the amount and quality of light falling on the objects.
Detailed, written documentation in the lighting plan, along with communication with the maintenance staff (in a maintenance manual) will help ensure that the bulbs of the same wattage, beam width, and color temperature are used for relamping. The angle of aim for each lamp fixture should also be recorded, and dimmers should be marked or fixed to prevent casual readjustment.
All light sources produce some amount of visible light, UV radiation, and IR radiation, but sunlight is particularly dangerous because it includes high levels of all three. In addition, daylight in an exhibit space provides light of inconsistent quality and quantity, changing with the time of day, season, and weather conditions. The complete elimination or tight control of sunlight not only serves a preservation function but is easier on the viewer.
Direct sunlight should never fall on light-sensitive objects. It may be necessary to block windows or sky- lights in the exhibit space or to redirect natural light entering the space from an atrium or adjacent area. Sunlight can be eliminated with architectural renovation, or blocked off, or mitigated or controlled with exhibit panels or light-filtering blinds, shades, curtains, or fabrics.
Controlling artificial illumination is a complex subject. The type of lighting systems, the wattage and color temperature of the lamps, the location and aim of the fixtures, and the use of diffusing filters and dimmers affect the amount of light falling on any object in an
exhibit. The exhibition designer has a wide range of lighting options within basic incandescent and fluorescent lighting categories, including surface-mounted track lighting, recessed lights, and fiber-optic systems.
Lamp locations directly affect the amount and quality of illumination falling on an object. Modifying the overall lighting plan, not increasing the amount of light, is the way to produce a desired effect. A few general precautions should govern decisions about location:
- Place fluorescent lamps at least 24 inches from displayed objects.
- Because of heat buildup and illumination levels, place incandescent or tungsten halogen light at least 36 inches from any object.
- Avoid locating a fixture too far from an object, or the conical beam of light will be spread too wide to provide effective illumination.
- When more than one light is used and the beams overlap, the amount of light reaching an object may be too high.
- Avoid shadows on objects and on the edges of framed pieces through careful location of fixtures and aiming of the beam.
Exhibit Design and Perception of Brightness
A gradual rather than an abrupt transition between differently lit areas is critical to making objects visible at low, restricted light levels. The human eye needs time to adjust from bright to low light. As visitors approach an exhibit area, the light levels to which they are exposed will influence their response to lower light levels inside the exhibit space.
It also helps to group light-sensitive objects away from exhibit entrances and points of bright light such as windows. The color of a wall or case interior, the texture, and the intensity of hue can affect the visibility of objects on display. Avoid sharp contrasts, because any juxtaposition of light and dark will lower viewing comfort.
Effects of Color Temperature on Perception
The type of light influences the way an object's color is perceived. Some exhibits attempt to reproduce a specific color rendering; for example, an artist may have painted under a certain type of daylight or artificial light. In general, however, most exhibit lighting plans try to achieve a color rendering close to daylight. Industry uses the color rendering index (CRI) to rate the color produced by a light source. The higher the CRI, the more balanced the light color. Some lamps produce cool or blue light, while others produce a warmer or yellow light.
The chromaticity values of lamps are rated according to color temperature (expressed in degrees Kelvin or °K):
- Lamps with a value of 3000°K and lower provide "warm" light that accentuates reds and yellows.
- Lamps of 4000°K or higher produce a "cool" tone that gives an overall blue-green cast.
- Lamps of around 3500°K are considered more moderate in tone and produce a white light. They are usually desirable for museum lighting purposes.
In general, simply dimming the lights usually causes a shift in the color rendering toward the warmer end of the spectrum. This can be a critical design mistake, making the human eye perceive the amount of light as even dimmer than the measurable level would indicate. Instead, for a lower light level without color distortions, choose a lamp with a lower wattage but a high CRI value and a moderate chromaticity value.
Constructing a simple mockup of the lighting design- including the fixtures, the various lamps, and the anticipated distances between the objects and lamps- prevents problems during installation. Light levels can be measured, and the designer, lighting specialist, conservator, curator, and other exhibition team members can evaluate the quality as well as the quantity of lighting. Based on testing of UV radiation emitted from the lighting mockups, the need for UV filters can be identified during this trial.
Although a mockup is recommended to complete the lighting design, monitoring with a light (footcandle or lux) meter during object installation is necessary to fine-tune light levels. Final lighting adjustments often involve some compromise between the conservation criteria and the public's ability to view the objects adequately.
- Examine objects or signs of infestation and active mold as part of the preliminary condition check. lf signs of infestation are found, consult a conservator about treatment options.
- Design exhibits to inhibit infestations. Make sure the exhibit area is insect-proof by screening open windows or doors, filling gaps in the building construction, and avoiding gaps and undercuts where dust can collect.
- Enclose objects. When the risk of infestation is high, place susceptible objects inside well-sealed cases or sealed acrylic boxes to prevent new infestation. Limit the gaps and holes to prevent insect entry.
- Avoid introducing insects through props and unchecked exhibit materials. Do not use wool carpets and other materials that attract and harbor insects. Avoid using organic exhibit props. Fumigate vegetative props or expose them to freezing temperatures before bringing them into the museum.
- Control human behaviors that encourage infestation. During exhibit production and installation and after the exhibit opens, never allow food in the object holding areas or the exhibit space, even if no objects are in the area.
Biological agents of deterioration can attack any object that contains plant or animal material. Even a small-scale infestation can cause significant damage if it goes undetected. Biological infestation includes damage caused by:
- insects such as wood-boring beetles, carpet beetles, silverfish, and moths;
- vertebrates (larger pests) such as mice and squirrels;
- microorganisms such as mold and fungus.
Make every effort to ensure that no infested objects or construction materials find their way into an exhibit. While examining each object, look for evidence of an infestation. Also inspect all materials before bringing them into the building, including construction materials, decorative elements or exhibit props such as vegetation. Knowing which insects and rodents are endemic to the geographic area is important in identifying a problem .
The standard practices of spraying and baiting for insects and rodents are not appropriate for collection areas. Talk with a conservator about using monitoring traps before using insecticides in an exhibit space. Organic objects that are very susceptible to infestation, such as textiles, natural history collections, and freeze-dried taxidermy specimens, require regular inspections. lf infestation is suspected, monitoring with strategically placed traps can help pinpoint the problem. A conservator can recommend appropriate control measures.
Exhibit construction should restrict pest entry and avoid introducing what pests need for survival: food, water and harborage. When designing an exhibit, take the following steps to prevent infestations:
- Maintain a moderate relative humidity (preferably below 60% RH and never above 75% RH) to discourage growth of mold and mildew.
- Eliminate moisture from leaks, floor drains, or other water sources near the exhibit space.
- Eliminate undercuts in cases and barriers that collect dust and make cleaning difficult. Accumulated dust and food are breeding grounds for insects.
- Keep light levels relatively low in exhibits, and place lights outside the display chamber of a case. Brightly lit areas attract some insects and adult stages of moths and dermestids, while other insect species and generally larval stages avoid light.
- Provide tightly sealed cases to prevent or deter pest infestation. Poorly sealed cases provide insects and rodents with an easy path to food; insect entry routes follow airflow, but gaps measuring smaller than 0.3 mm prevent entry.
- Do not plan an exhibit space that doubles as or is open to a food area. Ban food and drink from object holding and exhibit areas, especially during exhibit construction and object installation.
- Conduct a risk assessment. Identify the likelihood of theft and vandalism. Provide protection against human damage. Exhibits in a museum with a history of vandalism and theft may require additional security measures.
- Provide the appropriate level of protection. Tailor security features to the vulnerability of the objects. Highly vulnerable and valuable objects require more sophisticated protection measures than others.
- Use tamper resistant case hardware. Mount objects to panels or shelves, bolt freestanding cases to the floor, and lock exhibit cases.
- Facilitate authorized curatorial access to the objects. Each object in an exhibit should be readily removable without having to remove or disturb adjacent objects.
Providing sufficient staff to prevent theft, vandalism, and accidental damage is impractical for some institutions. Therefore, a well-designed exhibit is the first line of defense. Failure to design adequate security into an exhibit may have very serious consequences, including lost or damaged collections, damage to the museum's public image, and legal ramifications.
Perform a risk assessment for each exhibit. Different risks are associated with different objects. Consider the following examples.
- Objects with high monetary or collector value, such as firearms, jewelry, precious metals, coins, stamps, and small paintings, are often subject to theft.
- Statuary, artillery, and vehicles displayed in the open are likely targets of vandalism.
- Small, easily accessible objects, even when they have no real value, may be stolen.
- Historic documents or memorabilia associated with famous people or political events are often highly vulnerable.
In addition to reviewing the likelihood of vandalism or theft, a risk assessment surveys the exhibit space and museum building to identify vulnerabilities. Unalarmed emergency exits from the exhibition area, the lack of security guards, and small, easily pocketed objects displayed in the open are examples of situations that encourage theft and vandalism.
Additional security measures are required for an exhibit when the probability of the occurrence and the severity of the consequences together indicate a high risk. Common mitigation measures include security guards, motion detection, and alarms on doors, windows, skylights, cases, platforms, and even on individual large objects. At a minimum, alarms should be hard-wired to a monitoring company or the local police, with a power backup in case of power failure. Exhibit cases should be designed to allow them to be opened easily-during authorized entry-and closed safely by only one individual.
Protection against theft, vandalism, and damage must, of course, begin with securing the museum building. The building and exhibit space should be secured by:
- physically resistant construction;
- electronic devices to detect and deter criminal activity; and
- either constant human presence or a very rapid human response.
Displaying vulnerable objects in a case provides a certain level of protection. A wide range of security options can be designed into an exhibit case, including a dual case locking system, case alarms, and shatterproof or bullet-proof security glazing.
A case that provides a high level of security is necessary when displaying national treasures or objects of unusually high monetary value or political sensitivity. In addition, lenders may require certain security measures.
Since objects exhibited in the open are especially vulnerable to theft and vandalism as well as to environmental degradation, avoid open exhibits when possible. Open exhibits are the unavoidable norm in furnished historic structures. In such exhibits, securing small objects to larger ones or to architectural elements may be appropriate when it can be done without damage.
Importance of Human Presence
Although an area may be protected by security monitors, the presence of a guard or other trained personnel is the best deterrent to theft and vandalism. Providing effective but unobtrusive daytime security for exhibit spaces is critical. A daily walk-through by trained staff should include checking for building security as well as for maintenance problems, such as water leaks and pest infestations.
Staff awareness is critical to good exhibit security, so the exhibit budget should include funds for training. Even when museum staff members already know how to provide the necessary level of protection, they may need additional training to operate special security hardware or electronics. They may also need to learn crowd control techniques if the new exhibit is expected to draw heavier than normal attendance.
Emergency Preparedness and Fire Protection
- Develop fire protection and emergency response plans. The museum staff should have an emergency plan for each exhibit space. The plans should minimize threats to museum objects, protecting them during a disaster, during their evacuation, and after a disaster.
- Perform a risk assessment and address potential problems. Anticipate the types of damage that may occur to display objects. For example, avoid placing objects, especially if they are water sensitive, in the path of fire sprinkler heads.
Protection of exhibited objects from fire and natural disasters requires measures for the exhibit as well as the entire building. Increased security options which can be incorporated into exhibit design include:
- a fire detection system, and
- a water leak detection system.
Exhibit designs should facilitate:
- daily inspections of all exhibits (for object inspection and to identify preservation needs)
- regular preventive maintenance of the exhibit space (to forestall such problems as water leaks and HVAC system failures)
It is important to ensure that all exhibit lighting, electrical fixtures, and wiring comply with the National Electrical Code for both personnel safety and fire prevention. Unless the museum has adopted a particular edition, the exhibition designer should follow the latest edition. For detailed guidance see the National Fire Protection Association publication NAPA 909, Recommended Practice for the Protection of Museums and Museum Collections. Other measures include the following:
- Fire detector signals should be integrated into the building s fire alarm system.
- Alarms should be monitored by a manned fire department for quickest response.
- Display objects that are most sensitive to heat, smoke, or water inside well-sealed cases.
- Tall cases and exhibit panels must not obstruct air flow around heat and smoke detectors, nor should they block proper sprinkler discharge patterns.
- Where possible, the exhibition plan can specify the relocation of detectors and sprinkler heads to maintain optimum system effectiveness.
- Provide additional hand-held fire extinguishers within the exhibit space; they can be installed inside wall cabinets or exhibit case bases or concealed behind
- furniture in period rooms.
Optimum protection for exhibited museum objects
includes considering the risk of damage from earthquakes, hurricanes, explosions, floods, and other disasters. Cases, platforms, display panels, and other exhibit furniture must provide the optimum protection by their strength, bulk, and placement. Mounts for securing objects onto pedestals, platforms, or panels must be sturdy enough to prevent the objects from falling; they must also be attached so that they do not damage the objects during violent motion.
Exhibit design must allow the removal of vulnerable objects from the exhibit safely and expeditiously when a disaster is imminent. The need for prompt authorized access should be balanced against the need to prevent unauthorized access. When rapid access may be necessary, use locks and internal case alarms rather than screws on access panels and glazing to minimize entry time.
Exhibit Design Standards
The following standards are suggested for developing best practices for exhibitions within an institution. click on the Standards below to view the associated guidelines that expand on the topic.
The exhibit design plan must meet the Conservation Requirements for the exhibit objects
The exhibit design must utilize Exhibit Enclosures whenever possible and must always be carefully designed to promote object safety and fulfill the Conservation Requirements
Exhibit mounts and supports must be carefully designed to promote object safety and fulfill the Conservation Requirements
Design and selection of furnishings within the exhibit space must support object safety
Materials used within the exhibit space for construction, furnishing, decoration and interpretive settings must be object-safe
The exhibit’s physical layout [spatial design] must promote object safety
Effective conservation measures [design, controls and policies] must protect objects from harmful light exposure
Effective security measures [design, controls and policies] must provide the appropriate level of security for objects
Appropriate prevention measures must protect objects from fire and water damage
Appropriate measures [design, controls and policies] must protect objects from harmful exposure to pollutants
Effective measures [design, controls and policies] must maintain object-safe temperature and relative humidity
Appropriate measures must protect exhibit objects from damage by pests
This category has the following 4 subcategories, out of 4 total.
Pages in category "Exhibit Design"
The following 39 pages are in this category, out of 39 total.