Sachi Yanari-Rizzo, Curator of Prints & Drawings
Museums have many behind-the-scenes practices to maintain an environment that will minimize chemical and physical deterioration and promote the longevity of the art in the collection. This is sometimes referred to as preventative conservation. These policies are related to temperature and humidity, pests and pollutants, and lighting. They often relate to the etiquette, or rules, posted before entering museum galleries.
Some museums may discourage visitors from carrying coats, large bags, backpacks, and umbrellas. This is to prevent the works from being inadvertently hit, flecked with water, and from potential theft. However, museumgoers rarely need to wear a coat.
No matter what time of year it is, when you walk through museum galleries the climate pretty much feels the same. The goal is to maintain humidity and temperature at constant levels in the exhibition and storage spaces. Temperature that is too high can prompt the expansion of materials; whereas, temperature that is too low can cause embrittlement. Organic materials have the tendency to absorb moisture in high humidity, which can cause corrosion, mold, and insect activity. Low humidity can initiate shrinkage and cracking. At home, take into consideration that attics can present extreme temperatures. Bathrooms tend to be humid and basements can flood. Dramatic fluctuations in temperature and humidity can be a harmful cycle of swelling and contraction due to the extreme conditions.
Is there a magic number of temperature and relative humidity? Museums have to factor in that different art materials respond to environmental conditions in different ways because of their makeup. The visitors’ comfort is an important concern as well. Museums set a target temperature and humidity range knowing that there will be some minor fluctuations.
Museum staff checks monitoring equipment in the galleries and storage areas daily. Until more recent years, a distinct ticking sound could always be heard in the galleries as hygrothermographs measured temperature and humidity and made a record on paper. Their mechanism required weekly winding. However, these devices were largely replaced by electronic dataloggers connected to computers with software capable of producing charts and tables with the information.
No Flash Photography
Light can accelerate chemical and physical damage to artworks, which is irreversible. The most light-sensitive materials include works on paper, textiles, and natural fibers. Colors can fade, shift, or darken, and materials can become embrittled. Museums limit the duration of light exposure and control the light intensity and type of light. Of all the wavelengths, ultraviolet is the biggest culprit of light damage. Likewise, ongoing light exposure from flash photography can be detrimental to light-sensitive materials, such as drawings, prints, and textiles.
The measurement for light is in lux or footcandles, and is measured with a light meter. Recommended light levels for glass is 20 footcandles, in comparison with 5 footcandles for a watercolor. You may notice that galleries with textiles, prints, and drawings appear dim and the walls are washed with light rather than lit with a spotlight. These exhibitions tend to run only for 2-3 months. Some museums may have cases with motion-sensor lights or on timers for very delicate objects. History museums may display a copy rather than an original manuscript for a long-term exhibition. At home, you may reconsider hanging a work of art made of a light-sensitive material in direct sunlight.
No Food or Drinks
A commonsense reason not to permit beverages and food in the galleries is to avoid spills on the artwork.
Good housekeeping at the museum, like at home, is important for human health reasons and for the art. Homeowners don’t want to encounter mice or cockroaches in the kitchen, and the same is true at museums. Museums implement an integrated pest management plan with regular monitoring and practices like maintaining the building envelope, regular cleaning, trash removal, and prohibiting food, drinks, plants, and flowers in the galleries and storage areas. New works brought into the museum are placed in a temporary holding area rather than in collection storage.
An insect infestation can be damaging. Materials that may be tasty nourishment for insects include textiles and fibers, paper, and wood. For example, silverfish eat fabric, paper, and glue in bookbindings, moth larvae feed on wool, and powderpost beetles bore into wood.
Air quality is important and pollutants, like exhaust and tobacco smoke, can be harmful. When artwork suffers from smoke damage, the first thought may be that it was due to a fire. However, hanging a painting above a fireplace or in a home where the residents are heavy smokers can create a thin layer of sticky grime, causing the work to yellow.
Common sights at the museum may include staff members Michelle Cano, Maintenance Assistant, dust mopping, vacuuming, and regularly cleaning public areas; Leah Reeder, Registrar, gently using a feather duster in the galleries; or Brian Williamson, Technical Director, standing on the lift clearing off the cobwebs from the crevices on the Chihuly chandelier.
Dust can be a visual distraction, but routine cleaning is not just for aesthetics. These can be used as opportunities to take a closer check on objects to see if there are any changes in condition. Dust can be made up of traces of clothing fibers, plant fragments, pollen, human skin, hair, soot, and soil. Dust on art can cause physical abrasions or discoloration, become difficult to remove, and absorb pollutants and moisture in the air, which can promote chemical deterioration. The presence of dust may encourage mold growth and attract insects.
Good air filtration is beneficial, and even adding entry floor mats helps to keep dirt from tracking through the building. We can create physical protection from dust. For example, textiles and unstretched canvases are stored by rolling on a tube and covering with an acid-free tissue. Three dimensional objects stored on open shelving may be covered with acid-free paper or polyethylene.
Not all air pollutants come from outside the museum. Inside, materials such as wood, carpeting, and flooring can emit formaldehyde, nitric, and acetic acids. An example of mitigating this threat in storage is to replace wooden flat file for oversized prints for cabinets made of powder-coated metal.
Do Not Touch, No Pens
There is the obvious risk of physical damage by visitors continuously handling the artwork over time. By touching the art, dirt, body oils, and salts can transfer from your hands—another type of pollutant. Materials that look strong and sturdy can even suffer damage. Porous wood and stone can absorb the oils and darken. Fingerprints can lead to staining or corroding metal and the harm is irreversible.
While we ask visitors not to touch the artwork, this mantra also goes for staff as well. Staff try not to handle the artwork excessively, and often wear gloves when handling cannot be helped. Objects in storage are identified by tags or labels to decrease the need to rifle through things.
Look for upcoming blog posts on collections care and conservation. Helpful websites with guidelines on storage include the National Parks Service Conserve O Gram series and the Northeast Document Conservation Center’s resource pamphlets.