Alaskan Ten Agents of Deterioration

If you are reading this section on temperature as a threat to collections, you must also read the section on relative humidity (RH), because they are intimately linked. Warm air can hold more humidity than cold air, therefore changes in temperature cause changes in humidity. Often, it is the change in humidity that has the greater impact on collections preservation, but most Alaskan institutions do not have dedicated humidity control as part of their building equipment.

Conservator Pamela Hatchfield sums up the origins of the classic metric of museum preservation: “During World War II, the collections of the National Gallery, London, were stored for safety in a quarry in Wales. Conditions were maintained at a very stable 58% RH and 63°F. Significantly, documented observations revealed that no additional damage occurred during the five years in this stable environment, yet cracking, blistering, and flaking resumed when the collections were returned to uncontrolled galleries in London.” In the 1980s, the standard of 50%RH and 70°F was adopted by museums worldwide. These metrics determined what institutions would require in their loan paperwork and what museums needed to target for accreditation. However, many buildings and budgets struggled to achieve these standards in the practical world. In the 21^st century, issues of sustainability pushed museums to think more broadly about the recommended guidelines.

In general, collections always prefer cooler environments than humans. Part of the reason is the Arrhenius equation in chemistry, showing us that the rate of chemical reactions depends on temperature. For preservation purposes, this means chemical deterioration happens faster at warmer temperatures. Consider how sugar dissolves faster in hot tea than iced tea. Many chemical reactions double in rate for every increase of 10 degrees in temperature. At the Alaska State Museum, collections storage is kept at 60-65° F to slow deterioration. However, museum staff complain about how uncomfortable it is to work at 60° F for prolonged periods. Human comfort generally dictates the set point of our thermostats in most buildings, and typically occupied areas are around 70° F for human comfort.

While low temperature can aid preservation by slowing chemical deterioration, low temperatures can also cause damage. If we place objects in the freezer for pest control, or have collections in sheds and other structures with no climate control, there are risks. One risk is the formation of ice. While most objects do not have enough free water content to form ice crystals, occasionally there are fresh plant materials, fluid specimens, historic bottles with contents inside, and other liquids that might freeze. In addition to damage from sharp ice crystals, water expands approximately 9% when it freezes into ice. This expansion is the cause of so-called “freeze-thaw damage.” Another risk is embrittlement. Handling objects when they are cold is risky because many materials are more brittle at low temperature. Additionally, if cold objects are brought into a warm environment too quickly, condensation will form on their surfaces, which could also cause damage.

At the other extreme, high temperature can damage collections. Obviously, extreme high temperature from a fire can cause objects to burn. But heat sources such as radiators and light fixtures can also cause catastrophic damage such as melting plastics, shrinking wool or leather, and blistering paint. Elevated temperature can cause adhesives to slump or fail, and the surface of some materials may become sticky. Higher temperatures also increase the risk of mold, and are more hospitable to pests.

Recent advances in heat pump technology and funding incentives to install them have led many museums in Alaska to consider heat pumps as a solution to improve environmental control of collection storage spaces. Unless the heat pump also has the ability to remove humidity from the air, the overall amount of moisture in the space is not decreased and the preservation environment is not improved. Many sheds, garages, and outbuildings are poorly insulated and experience conditions similar to the outdoors. Heating those spaces will not improve the overall humidity situation because of the way humidity is simply relative to temperature. Here is a pdf describing the case of how a heat pump might work in a shed in Southeast Alaska.

In order to advocate for the improvement of less-than-ideal spaces, it helps to collect data on the true environmental conditions collections are experiencing. Sometimes, buildings have sensors that give electronic data about a building’s HVAC system. The facility manager of a building can usually access this information. However, those sensors are not always located where the collections are physically situated. More often, they are located inside the duct work of the building. Most museum collection managers use portable data collection equipment to monitor the temperature and humidity in various locations collections are stored and exhibited. These include PEM2 dataloggers (figure 1), HOBO dataloggers (figure 2), hygrothermographs (Figure 3), psychometers for immediate readings (figure 4), and non-recording options such as Arten thermo-hygrometers and humidity cards (figure 5).