Alaskan Ten Agents of Deterioration

Light is an agent of deterioration because it is energy that can break chemical bonds. Common damage resulting from excessive light exposure includes fading of sensitive colors, yellowing of paper, and embrittlement of organic materials. Many people are aware that ultraviolet (UV) light is the most damaging wavelength of light for collections. This can be controlled by avoiding natural daylight and using UV filters on lighting fixtures and UV protective glazing on framed artworks. However, ALL wavelengths of light are damaging. Controlling UV alone is not enough. Figure 1 shows a blue folder that was exposed in a window for two months. A strip of aluminum foil blocked all light, a strip of UV filter blocked some light, and one strip had no filter. Fading from full exposure was very similar to fading with a UV filter. Both were significantly more faded than the foil-covered area.

How do we measure light levels? A light meter (figure 2) is a device that measures light in footcandles or lux. A footcandle is a unit of measure: the light intensity produced by one candle at a distance of one foot. Lux is the metric version, and one footcandle equals approximately 10 lux. Many light meters read in both.

Typically, museums set the lowest level of lighting at 5fc for things like watercolor paintings, natural dyes, and color photographs. Lower than 5fc would be nice for the objects, but makes it very hard for visitors to see them clearly. The upper range of light levels are around 30 footcandles for things that are not light sensitive at all, like stone sculptures and things made of metal. In between are most things made from plant or animal sources. Good museum practice uses a light meter to set light levels for every exhibit. A light level recommendation is assigned to each item when the Alaska State Museum exhibits or loans collections. This pdf lists the light levels selected for each item displayed in the inaugural exhibits of the new Andrew P. Kashevaroff building that opened in 2016.

In this document, materials are listed under different recommended light levels with a published reference of why that light level was selected. At the end of the document is an annotated bibliography of sources. One common method to evaluate exposure over time involves blue wool fade cards (figure 3). A fade card has several strips of wool dyed blue with progressively more sensitive dyes. A card is cut in half, with one part kept in the dark and the other put in the test location exposed to light. After a period of time, the two are compared and the exposure correlates to how much fading is seen compared to the control piece kept in the dark. Many small museums find it difficult to keep track of those cards, and staff turnover makes it even trickier.

How do we measure fading? There are several ways to monitor fading, but two main approaches are to establish a baseline reading and keep checking for signs of change over time, or to induce a tiny pinpoint of intentional fading to establish the true vulnerability of a specific colorant. Colorimeters and microfade meters are expensive analytical devices that some large museums use to collect that data. The Alaska State Museum uses Munsell color books, which contain reference swatches of specific colors that are matched to collections items as a baseline and then repeated later to check for change (figure 4). The decision to use the Munsell system is shown in an internal memo with pros and cons of various systems to monitor fading.

Light damage is cumulative and irreversible. For items that are light sensitive, caretakers must decide how fast an item will be damaged. Is it kept for future generations, or used up sooner? Low light levels and infrequent display can prolong the useful life span of an item. Some strategies include:

• Exhibit reproductions instead of originals
• Open a show with originals and rotating out to reproductions
• Avoid shining a beam of light directly on a light-sensitive item
• Use fewer light fixtures
• Move light fixtures further away
• Use filters on light fixtures
• Use dimmer bulbs
• Use protective glazing on artwork
• Max out light levels in exhibit spaces at 30 footcandles to help eyes adjust to low light levels
• Use curtains that must be lifted by patrons to view the item
• Install motion sensors that turn on lights only when people are in the area

Balancing the needs of preservation versus access for the collections we care for is a difficult compromise. An example of one approach is the 2016 Light Fading Plan explored for new exhibits at the Alaska State Museum.

Sometimes interventions are expensive and must be justified in order to muster the resources needed to protect collections. One example is the cost of protective glazing for light sensitive artworks that were installed for the inaugural exhibition of the new Andrew P. Kashevaroff building. A memo was written to justify the expense, which helped supervisors and leadership advocate for the needed materials. Also helpful are examples of real damage (Figures 5-7).

Because light is an agent of deterioration, keeping lights off in gallery spaces and collections storage spaces whenever possible is a good habit. All organic materials suffer from deterioration with light exposure, and things made from plant and animal sources should be protected from unnecessary light.