No one can dispute that the physical and ambient environments in which cultural heritage collections reside have a significant impact on their long-term preservation. Throughout the twentieth century, the emerging conservation science and conservation/ restoration professions tried to establish what exactly constitutes a safe environment.

Scientific research, together with observations in the field, increased understanding of the agents of deterioration and their workings, and these findings led to the specification of environmental parameters in guidelines and standards. As these became universally accepted and implemented, they also became more rigid over time, resulting in a one-size-fits-all approach.

With the current need to adapt to global climate change and to deal with the impact of the serious budgetary pressures faced by collecting institutions, such an approach has been found to be unsustainable. In recent years, the international conservation field has been challenged to review and revise these long-held positions. To understand how the field is currently responding to changing times — and why and how experience, perceptions, and uncertainty appear to influence positions — it is important to appreciate how the concept of the museum environment has developed since the late nineteenth century, and how several milestones of technical research and experience informed the environmental guidelines of the late twentieth century.

museum environment milestones

The control of the indoor climate of museums has a long history, but it was not until the early twentieth century that museums attempted yearlong humidity control. In 1908, the Boston Museum of Fine Arts was the first US museum to try this, settling upon a relative humidity (RH) of 55%–60%, based on trials conducted over two years. Then in 1915, the Cleveland Museum of Art installed a humidification and heating system set to maintain 50%–55% RH, also experimentally determined to be optimum. Although these experiments were not published in detail, they seem to be the earliest instances of humidity specifications for the museum climate.1

As air-conditioning systems were adopted by museums, discussions followed about the suitable range of control for the museum environment. The first International Conference for the Study of Scientific Methods for the Examination and Preservation of Works of Art in 1930 resulted, ten years later, in the publication of the Manual on the Conservation of Paintings, authored by a panel of international experts, including Harold Plenderleith and George Stout. Even with a better understanding of the environmental agents of deterioration, the experts suggested a pragmatic approach. The panel wrote: “We have no adequate information at present to enable us to fix an absolute standard. The reason for choosing 60 to 65% as the figure for relative humidity for practical purposes is that in many climates it is the nearest approach to the conditions in which a degree of stability may be easily obtained. […] In a temperate climate, 60% of relative humidity is the easiest standard to keep up. At normal temperatures, this represents comfortable conditions for the human organism. […] It may thus be assumed that atmospheric conditions at present considered normal for the majority of objects in museums will also be acceptable to visitors.”2

An increased understanding of the effects of indoor climate on vulnerable materials was the result of efforts to evacuate and protect the collections of Europe’s great national museums during both world wars. Stable conditions—such as those created in temporary storage in adapted mines in the United Kingdom—were found to reduce the time spent on maintaining the artworks. Those conditions were around 17°C/63°F with RH around 58% for Manod3 and 15.5°C–23.8°C/60°F–75°F with 60%–65% RH for Westwood Quarry.4

After World War II, science established its place in the museum world, and as deterioration mechanisms were better understood, interest grew in what we now call preventive conservation. In 1949 at the American Association of Museums conference in Chicago, George Stout advocated “long-range conservation.” The care of museum objects, he said, is “as much concerned with things which are evidently in a good state as with things which are conspicuously in a bad state.” He went on to say that, “It would be impossible to figure the cost of neglect against the cost of constant care and protection, but it does not take much imagination to see that consistent care will save money as well as the integrity of objects. […] There may be those who think that the care of a collection is only a matter of occasional repair. […] Conservation is merely the business of trying to prevent undue deterioration. This effort requires the best available knowledge of the true state of the thing that is subject to deterioration. It requires further that every attempt be made to keep that state as it is.”5

In 1960, Harold Plenderleith and Paul Philippot published the results of a 1955 international ICOM survey on the effects of climate on the conservation of museum objects. Their report, “Climatology and Conservation in Museums,” provided a fairly wide “zone of safety,” as the authors called it, placing the RH range as 50%–65% but noting that RH should not undergo abrupt changes. They also stated that object safety depends on its past history, its structure, and the conditions to which it has become acclimatized. The authors acknowledged that “even the best museum conditions can be dangerous for a painted panel that has been normally housed in a cold damp country house.” The report also mentioned, possibly for the first time, risk as a factor in determining an environment for a collection: “A rational system of conservation will, then, be based first of all on a thorough assessment or diagnosis of the risks inherent in the milieu in which objects are placed.”6

In 1967, the International Institute for Conservation (IIC) organized in London the first conference on museum climatology. In the preface to the conference publication, N. S. Brommelle, IIC’s secretary-general, described preventive conservation: “The study of how the environment in a museum affects its contents, and of how to ensure that their inevitable ageing processes are slowed to a minimum has become to be called Museum Climatology. […] Today just as in medicine, the ultimate objective is seen to be the prevention of disease. Hence fair proportion of the best scientific and technical work in museums is coming to be devoted to the subject of museum climatology.”7

pragmatic preventive conservation

The pragmatic preventive conservation approach prevails as an outcome of these earliest discussions of the museum environment. Scientists at museums had a profound influence on the profession’s early understanding of the interrelationship between the environment and deterioration. While they did not shy away from suggesting a temperature or RH range, greater emphasis was often placed on avoiding climatic extremes (especially extreme fluctuations), rather than precisely hitting a specified climatic range. The term “optimal conditions,” which appears frequently, is never associated with an absolutist vision of what constitutes a “zone of safety,” to use Pleinderleith and Phillipot’s wording. Local climate mattered. Historical conditions of objects mattered. And “optimal conditions” did not refer to a universal standard; it was something that could be defined locally.

This pragmatism is also an undercurrent in the work of the man whose name is virtually synonymous with the museum environment—Garry Thomson. He is often considered the scientist who gave conservation clear and indisputable specifications for the environment, but this characterization is inaccurate. In fact, Thomson was as much a pragmatist as the scientists who came before him. He argued for choosing an RH level according to climate zone: “An air-conditioned museum should reflect average indoor RH at the locality. The old objects of local origin will have been made in this climate and will have adapted to it […] keeping near the local RH results in economy of energy use.”8

Thomson also foresaw what would eventually lead to a standardized approach for loans: “Most museums these days […] will borrow and lend. For the larger museums this implies exchange between countries, possibly of very different climate. The lending museum may very properly demand conditions reasonably close to its own. This will strengthen a trend towards median RH values (50 or 55%).”

Few will disagree that the narrow environmental parameters pursued by many museums in recent decades were influenced by the very thing that Thomson alluded to—the facilitation of loans from one climatic zone to another. A single environmental specification for temperature and RH neatly eliminated the trouble of taking into account the climatic history of the object, as well as a number of other considerations, including whether borrowing or lending institutions were actually able to maintain such conditions.

Were loans the only factor in establishing the narrow environmental specifications museums have long favored? Or were other forces at play, and were other voices influencing the discussion? The 1970s saw the start of a several-decades-long museum building boom, which included renovations and expansions, as well as new buildings and other capital improvements. Architects and engineers had to design ever more sophisticated buildings and systems, and they demanded target numbers for engineering and designing purposes. In major building projects, conservators often participated during the planning stage and thus had some input, but “designing to the numbers” soon took hold, and as it did, architects and engineers became major shapers of the museum environment.

This shift was aided by conservators who, at least initially, found reassurance in a published set of numbers that seemed definitive and that could be applied almost universally. Best of all, by handing over the numbers to climate systems designers, they could get tightly controlled environments, applying the “best available technology,” designed to minimize the risk of damage. HVAC technology had grown more reliable, permitting people to think that “if tight control is good, tighter is better.” Museums in general appeared to have sufficient resources to maintain tight control, and there seemed to be plenty of fuel to keep systems running. Sustainability was a concept that rarely crept into museum life.

However, there were some who expressed concerns for the impact of these tight controls on museum buildings. Stefan Michalski recalls: “In 1979, after recognizing that most Canadian buildings […] could not sustain winter levels of 50% relative humidity (RH), CCI advised Canadian museums to consider a seasonal adjustment from the summer setting of 50% RH down to a winter setting of 38% RH.”9

Over time it became apparent that tight control was often difficult to achieve and maintain within certain buildings, as well as within certain budgets. Moreover, some began questioning whether it was even necessary. In the early 1990s, research carried out at the Smithsonian Institution indicated that some materials were likely more resilient when subjected to wider ranges of RH. The significance of this new discovery lay in its potential to save millions of dollars in construction and energy costs.

These other viewpoints were widely, and sometimes fervently, discussed, and they raised important concerns for the field to confront. The debate about the museum environment might have remained an internal one that conservators conducted among themselves with occasional insights from scientists or HVAC engineers; however, once museum directors weighed in, the debate expanded dramatically.

current viewpoints

In 2008, directors associated with the International Group of Organizers of Large-scale Exhibitions—also known as the Bizot group—kick-started a complete rethinking of the environmental specifications for museum objects on loan, stating that museums should stop imposing standard environmental conditions. Urging consideration of sustainability, the Bizot group called for new guidelines with broadened environmental parameters.

The conservation field has responded. Professional bodies representing conservators at the national and international levels have developed interim guidelines, balancing points about sustainability raised by directors with preservation concerns expressed by conservators. The American Institute for Conservation of Historic and Artistic Works (AIC) Environmental Guidelines Working Group drafted interim guidelines for loans that were presented to the Association of Art Museum Directors meeting in 2012. The same year, the Bizot group unanimously adopted a set of Guiding Principles and Interim Guidelines, and the British Standards Institution released PAS 198:2012 — Specification for Managing Environmental Conditions for Cultural Heritage (basically, a kind of interim standard). In April 2014, the Australian Institute for the Conservation of Cultural Material published interim guidelines based on those developed by international professional conservation groups such as AIC.

It is interesting that these guidelines are all “interim,” as if we are waiting for confirmation of their appropriateness. Is it because we realize that guidelines like these do not address the full range of issues associated with the museum environment? Or because they don’t seem to reflect a widespread consensus within the field? Discussions surrounding the question of whether environmental parameters should be revised—and to what extent—raise the valid concern that there may be insufficient understanding of the reactions of some materials to environmental changes, especially materials in composite objects.

Today, even though there is agreement in conservation that museums must contribute to reducing their carbon footprint by implementing sustainable strategies, there are different viewpoints about how to achieve this and at what cost to collections preservation. While the reasons behind any professional opinion are generally complex and nuanced, current discussions of what constitutes an appropriate museum environment often reflect clear and definable attitudes toward risk. These attitudes are at the core of three distinct positions currently found in the field; these can be described as precautionary safety, proven safety, and pragmatic risk management.

Precautionary Safety

The precautionary safety stance derives from the precautionary principle, as applied in public health and environmental law. It holds that an action or policy that may prove harmful, even without full scientific proof that it is harmful, must nonetheless be avoided. A proponent of precautionary safety in conservation might consider a wider range of RH an unacceptable risk because there is not enough scientific evidence that materials will not be adversely affected. This stance argues that a single target of RH and temperature, combined with the smallest specifiable fluctuations, is the only confirmed path to unconditional safety.

This position remained strong through the 1970s, ’80s, and ’90s, and today it is supported by several institutions, such as the Doerner Institut in Munich. The Doerner issued a 2014 statement called “Stable Is Safe: The Munich Position on Climate and Cultural Heritage,” in which it opposed the interim guidelines and argued that “a reduction in the ecological footprint of our institutions can be achieved far more effectively, and with no risk to the cultural heritage in our care, by other means. […] The Interim Guidelines increase the risk for all lenders.”10

But it is not at all certain whether an absence of visible damage in a strictly controlled environment is, in fact, the result of a high level of climatic control. Colleagues in museums that do not have stringently controlled environments have also observed a lack of visible damage due to climatic factors. Having experienced this phenomenon, some conservators have adopted a different attitude—they endorse the concept of proven safety.

Proven Safety

The proven safety stance argues that even in museums with stringent environmental specifications, the conditions that are actually maintained have ranged outside these specifications, yet reports of noticeable damage are infrequent. Many conservators have conceded that their own museums cannot do better than 40%–60% RH and 15.5°C –25°C (60°F–77°F). Those experienced with traveling exhibitions attest that their objects routinely survive such ranges without apparent harm. These de facto conditions therefore appear to be safe. The proponents of proven safety were among the first adopters of the concept of “proofed fluctuations” when it was introduced by Stefan Michalski (this concept, simplistically put, uses the past experience of an object as a determinant of whether future damage is likely). They also share kinship with those who first wrote about the museum environment, placing an emphasis on the avoidance of extremes and fluctuations, and on a consideration of local conditions.

Pragmatic Risk Management

In the 1990s, risk management gained a place within conservation, having migrated from the public policy, health, and insurance industries. The pragmatic risk management stance argues that the goal of preservation is the minimization of loss due to a variety of causes, and that for each cause—such as an inappropriate environment—the decision maker needs to know the quantitative interrelationship among the intensity of the hazard (e.g., climate fluctuations), the damage caused (e.g., cracks), and the cost of controlling the hazard (financially, environmentally, and socially). Priorities are identified and decisions are based on significance or value assessments. This kind of thinking is reflected in the chapter on museums and archives in the ASHRAE Handbook, as well as in PAS 198:2012.

Although the proven safety stance is compatible with this perspective, pragmatic risk management goes further and recommends that resources be applied toward reduction of the biggest risks, which may not in fact be climate fluctuations.

These three positions are by no means static — conservators may well find themselves moving from one stance to another. It may be that one believes in theory that a pragmatic risk management approach is more sustainable but feels insecure in implementing it in practice because of a lack of information or experience. It is only human to take a precautionary approach.

This partitioning of the debate reflects the confusion many of us face with respect to making appropriate decisions both for our collections and for the cause of greater sustainability. But despite the differences in opinion, the conservation community has confronted these issues. Professional bodies such as AIC, ICOM-CC, and IIC have provided platforms for discussion and exchange of ideas and experiences by facilitating conferences and meetings. Not only has more scientific research been initiated, several museums, libraries, and archives have taken leadership roles in implementing new climatic strategies. It looks promising that energy efficiency and appropriate climatic conditions for collections may be shown to be compatible, making sustainable collection care more widely achievable.

Foekje Boersma is a GCI senior project specialist. Kathleen Dardes is head of GCI Education. James Druzik is a GCI senior scientist. This article is based on the paper “Precaution, Proof, and Pragmatism: 150 Years of Expert Debate on the Museum Environment,” which was presented by the authors at the 42nd Annual Meeting of the AIC in June 2014.

1. J. P. Brown and William B. Rose, “Development of Humidity Recommendations in Museums and Moisture Control in Buildings,” 1997.
2. International Council of Museums (formerly International Institute of Intellectual Co-operation), Manual on the Conservation of Paintings (London: Archetype Publications, 1997), 58.
3. David Saunders, “The National Gallery at War,” MRS Proceedings 267 (1992): 101–10.
4. Marjorie L. Caygill, “The Protection of National Treasures at the British Museum during the First and Second World Wars,” MRS Proceedings 267 (1992): 29–40. 5. George L. Stout, “Long-Range Conservation,” The Museum News (American Association of Museums), vol. 27, no. 5 (1949): 7–8.
5. George L. Stout, “Long-Range Conservation,” The Museum News (American Association of Museums), vol. 27, no. 5 (1949): 7–8.
6. Harold J. Plenderleith and Paul Philippot, Climatology and Conservation in Museums (Rome: International Center for the Study of the Preservation and Restoration of Cultural Property, 1960), 248, 253.
7. Garry Thomson, Contributions to the London Conference on Museum Climatology 18–23 September 1967 (London: International Institute for Conservation of Historic and Artistic Works, 1968).
8. Garry Thomson, The Museum Environment (London: Butterworth Heinemann, 1978), 112.
9. Stefan Michalski, “Museum Climate and Global Climate: Doing the Right Thing for Both,” in Reflections on Conservation (Ottawa: CCI, 2011), 9.