7  Background

The Museum records three kinds of environmental data: temperature (℉), percent humidity (%RH), and dew point (℉). These data are collected with EasyLog EL-SIE-2+ data loggers (Figure 7.1). See Section 7.1 for suggested ranges of temperature and relative humidity.

From the standpoint of data analysis and visualization, environmental data are a kind of time series (Kitagawa 2020; Hyndman and Athanasopoulos 2021). Therefore, Craig used the xts extensible time series library (Ryan and Ulrich 2022) and the dygraphs time series plotting library (Vanderkam et al. 2018), which is a wrapper for the dygraphs JavaScript library.

(a) Basement logger

Figure 7.1: University Museum data loggers

7.1 Guidelines for Museum Temperature and Humidity

Garry Thomson’s (1990) The Museum Environment represented an important early work dealing with temperature, humidity, and dew point (along with light and pollutants). In terms of temperature, Thomson (1990, 268) suggests a Winter range of 64.5-68 (℉) and a Summer range of 73-77(℉). With respect to humidity, Thomson (1990, 119) writes:

“Choice of RH level depends on several factors but cannot go too far from 50 or 55% RH. An exception may be found in the very low winter temperatures of Canada and north-eastern Europe where attempts at humidification to this level may endanger the building. The tolerance usually quoted of ± 4 or 5% RH is based more on what can be expected of an air-conditioning plant than on what exhibits can actually stand without deterioration, which is not known in any detail.”

Thomson expected these values to be refined with further study.

In April 12-13, 2010 a seminar entitled “Rethinking the Museum Climate” was held by the Museum of Fine Arts (MFA), Boston and the Getty Conservation Institute at the MFA, Boston. A major thrust of the meeting was to rethink museums’ carbon footprint in light of climate change. Out of the meeting came a proposal to revise the standards developed in the early 20th century (Thomson 1990).

Later that same year, at the 2010 American Institute of Conservation (AIC) meeting the 3rd International Institute for Conservation of Historic and Artistic Works (IIC) Roundtable on “Dialogues for the new Century” held “The Plus/Minus Dilemma: The Way Forward in Environmental Guidelines” (transcript and video). The aim of this oft-cited discussion was to evaluate the existing standards for collections environments. If one can glean a consensus from the discussion, it was that many institutions struggle to remain within the previously established thresholds, and that these thresholds may need to be adjusted depending on the materials and the region. This seems generally consistent with Thomson (1990).

In 2014, Foekje Boersma, Kathleen Dardes, and James Druzik (2014) crafted a historical review of major trends in the management of museum environments. The document emphasized the “need to adapt to global climate change and to deal with the impact of serious budgetary pressures faced by collecting institutions” while ensuring the environmental safety of the collections. Their summary presents thee common stances: precautionary safety, proven safety, and pragmatic risk management. The “precautionary safety stance” that comes from public health and environmental law which holds that actions that may prove harmful, even without full scientific proof of those harms, should be avoided. They describe this as the prevalent position from the 70-90’s. The “proven safety stance” asserts that even museums that seek to maintain tight environmental controls still exhibit conditions that fluctuate outside of specified ranges, and reports of noticeable damage are infrequent. Conservators operating from this stance emphasize avoidance of extreme fluctuations and place consideration on local conditions. The “pragmatic risk management stance” emerged in the 90’s and was an adoption of rationales from public policy, health, and insurance industries. This stance asserts that the aim is to minimize loss and evaluates a variety of factors including hazards (like fluctuating conditions) in relation to possible damages caused (like cracks) and the cost of controlling the hazard (including financial, environmental, and social costs).

The National Park Service’s Museum Handbook recommends that, where comfort of humans is a factor, most collections should be kept in conditions between 59-77 (℉) and 45-55% RH (Bacharach 2019, 4:22, 4:27). The manual further notes that it is important to avoid extreme changes in either temperature or RH.

The American Alliance of Museums, Museum Registration Manual (6th) (Simmons and Kiser 2020) chapter on “Preventative Care” (Bauer Kilgo 2020, 506) says:

Traditionally, a universal standard of 70°F ± 5° and 50 percent relative humidity ±5 percent was encouraged for all collection storage. Although this standard was once a good rule of thumb, the emphasis now is on establishing set points for temperature and relative humidity that are based on the materials the collection objects are composed of and what the building heating and cooling systems can reasonably maintain with minimal fluctuations in a particular geographic area.