One of the most important concerns of conservators and curators is the museum climate in which their objects are displayed or stored. This is not without reason. Everybody has seen damage, such as cracks in wooden furniture and warped and/or cracked panel paintings, attributed to improper environments. Loose veneer and flaking paint are also often blamed on climatic fluctuations.

Even though the mechanisms behind environmentally induced damage to wooden museum objects—and museum objects generally—are understood to an extent, there is still uncertainty about the point at which damage actually occurs. Conservators and curators tend to speak of a good or a bad climate, but no one is really certain when a climate is "bad," because we cannot predict exactly when damage will occur. We tend to draw conclusions from climate graphs without really knowing when objects are at risk. Why do we look at graphs rather than at objects? Probably because they are easier to read than objects. Of course, once an object shows new damage, it is too late. But if objects are not monitored, how do we know if the damage is new and when and under what circumstances it occurred? Given the high cost of climate installations and the damage that they may inadvertently cause, there is urgent need to develop a clear understanding of the relationship between the museum climate (recorded in climate graphs) and the response of museum objects. It is noteworthy that research related to this relationship has rarely included systematic analysis of the behavior of museum collections. Analyzing large groups of museum objects could give the museum community much insight into the reaction of objects to variations in their environment.

climate, risk, and sustainability

Because of observed damage, the museum community adopted strict climate specifications in the last century, such as a relative humidity (RH) of 52 ± 2%. In recent decades, there has been a tendency to relax these specifications slightly. Still, these broader climate specifications, which generally allow for seasonal fluctuations as well as a range of ± 5% RH, remain quite strict. Recent research indicates that these revised specifications will not result in damage, but the findings have yet to fully convince the museum community. The involvement of conservators and curators in systematically monitoring museum objects instead of only looking at climate graphs is essential in developing more rational guidelines for climate specifications.

A related question (which might either complicate or simplify matters) is how much risk we are prepared to take. Museums and conservators do not wish to take any risks with their objects—but perhaps that is not the best way to avoid risks. Because it is not clear when climate damage will occur, avoiding risks at any cost actually might increase risks. For example, the failure of an extensive air-conditioning system may result in abnormal conditions. Damage to historic buildings can be caused not only by the accommodation of air-conditioning, but also by excessive moisture buildup in walls or heavy condensation on windows. Costs for installation, maintenance, and energy consumption are high. Perhaps the limited funds of museums would be better used for other purposes. We could employ more staff, buy objects to enhance our collections, and improve visitor facilities. It is important to know how much climate risk we actually take and to weigh this risk against other threats such as theft, vandalism, and accidents.

Striving for a "greener" environment and reducing energy consumption is, fortunately, achieved not only by widening climate specifications. Much energy can be saved by designing "greener" buildings and improving the energy efficiency of systems in existing buildings. Museum climate graphs often resemble shark teeth; this pattern implies that air-conditioning systems are constantly overreacting. It would be sufficient to bring RH and temperature back into safe ranges instead of returning them to their initial settings. Systems can be switched off in daytime if climate conditions are moderate or turned off at night when buildings are not in use.

Although conservators probably belong to the group most concerned about climate effects, the bulk of research seems to have been carried out by engineers and conservation scientists. This research is mostly performed in laboratories, with mock-ups made of new materials—or by the study of single museum objects. For obvious reasons, groups of museum objects are not used for experiments in climate chambers. Engineers and conservation scientists are less familiar with the actual behavior of museum objects because they usually have little access to museum collections and do not have the specific knowledge and experience that conservators have. For their part, while conservators have less knowledge of physics, engineering, and the technology of wood, their knowledge, intuition, and experience should not be underestimated in discussions about climate. Questions or even skepticism that conservators have about work by engineers or conservation scientists should be taken seriously. It is equally important for conservators to respect and try to understand the work of engineers and conservation scientists. Moreover, conservators must assume a responsibility to be engaged in the climate research.1 It is essential for professionals from different backgrounds to make the effort to understand one another in order to share their knowledge. Only then might the whole field agree on new climate specifications.

research on objects

As noted, relatively little research has been carried out on groups of museum objects.2 In 2011 a Getty-funded experts meeting at the Rijksmuseum about setting a research agenda for the conservation of panel paintings recommended making information available on changes in condition and conservation treatments of large numbers of objects.3 The 2012 "Climate for Collections" conference in Munich included some studies about groups of objects. These studies included the relationship between the fuel bills of Swedish churches and damage to church furniture,4 damage development in veneered furniture at the historic Kenwood House,5 climate effects on the furnishings in Linderhof Palace,6 and, as a prelude to the Climate4Wood project, a preliminary study of actual museum objects.7 Each study reflected the difficulty in detecting new damage and included a variety of techniques to monitor and quantify it.

The Climate4Wood research project is an example of the kind of study of groups of museum objects that can provide insight into the museum environment issue. The research itself is a collaboration among the Rijksmuseum, Eindhoven University of Technology, the Cultural Heritage Institute of the Netherlands, and Delft University of Technology, funded by the Science4Arts Program of the Netherlands Organisation for Scientific Research (NWO). This program funds six collaborative projects among museums and universities to develop a new perspective on conservation.

Climate4Wood performs research on the effects of climate fluctuations on panel paintings and decorated panels in furniture. Panels were chosen as the subject because they are considered to be highly sensitive to climate fluctuations. The two main parts of the project are the Museum Study, carried out by furniture conservator Stina Ekelund and started in December 2012, and the recently begun Modeling Study by constructional engineer Rianne Luimes. For the Museum Study, the construction, materials, and damage development of a large number of Dutch cabinet doors in the Rijksmuseum collection are being systematically analyzed. In fall 2014, the same analysis will be carried out on the Rijksmuseum collection of panel paintings. The results will be compared to various well-documented objects in other collections. The parameters from the Museum Study are used as input for and verification of the Modeling Study, which will model climate- and age-induced stresses and deformations. Together with experimental research and in situ monitoring, this collaborative project should give us a better understanding of the mechanisms of damage development, with the goal of making an important contribution to formulating sustainable climate guidelines.

The Museum Study has already delivered some interesting preliminary results.8 The construction of around one hundred pieces of furniture, the properties of the materials used, and their condition were analyzed in detail. Shrinkage is usually 1% of the original width in seventeenth- and eighteenth-century panels, with the exception of thin (6–8 mm) restrained panels, which survive with virtually no damage. Most interesting and relevant is the observation that objects with similar construction and materials have identical damage patterns. This finding is interesting since the objects entered the Rijksmuseum from different owners and therefore do not share the same climate history. One might have expected the observed damage to vary widely, but the observed damage is identical. Perhaps the objects’ specific climate history is not so relevant. Or is it possible that the accumulated climatic experience of the cabinets was similar before they entered the museum?

Furthermore, the furniture panels have not suffered any climateinduced damage since they were photographed upon acquisition. Even cabinets that have been in the Rijksmuseum for over one hundred years do not show development of this kind of damage. Cabinets in historic houses, with identical construction to those in the Rijksmuseum, have identical damage patterns, which appear stable. The climate history of the galleries in the Rijksmuseum has not yet been researched, but it is known that the RH could sometimes reach extremes of 45% or 70%. It is a paradox that we consistently witness shrinkage cracks of approximately 1% of the original width, but that this shrinkage process seems to have stopped at some point. Does new damage only occur in extremely unusual conditions? In the former furniture conservation studio, which was housed in the Teekenschool, a building separate from the museum—a single brick wall structure with single-pane glass, central heating, and mobile humidifiers—RH was known to drop below 30% during very cold weather. When the canals were frozen, occasionally (but not always) new hairline shrinkage cracks appeared.

Another important observation, also highly relevant to the Modeling Study, is that shrinkage cracks are nearly always glue joints that have opened up. Cracks within a single board are rare. This finding suggests that engineers who model a panel in the future should include glue joints in their planning.

Although it is too early to draw major conclusions, the systematic study of large groups of real objects, carried out as part of the Climate4Wood Museum Study, has already provided interesting new information. The shrinkage cracks that caused concern about climate conditions actually occurred before the objects entered the Rijksmuseum and are consistent among objects with the same construction and materials. Perhaps the Modeling Study can provide us with an explanation. The study of the Rijksmuseum panel paintings planned for 2014–15 will undoubtedly offer other valuable insights.

Future climate research in the context of the museum environment should, like the Climate4Wood studies, focus on the systematic study of large groups of real objects. At the same time, it is important that conservators fully participate in this research, as they have the knowledge and experience required to analyze groups of objects. Collaboration with engineers and conservation scientists is essential in the effort to establish climate guidelines that will gain ultimate acceptance throughout the entire field.

Paul van Duin is the head of Furniture Conservation at the Rijksmuseum and is one of the coordinators of Climate4Wood, which seeks to establish a safe and sustainable museum climate for panels.

1. Sarah Staniforth, "Environmental Conditions for the Safeguarding of Collections: Future Trends," Studies in Conservation 59, no. 4 (2014): 213–17.
2. Jo Kirby Atkinson, "Environmental Conditions for the Safeguarding of Collections: A Background to the Current Debate on the Control of Relative Humidity and Temperature," Studies in Conservation 59, no. 4 (2014): 205–12.
3. Nico Kos and Paul van Duin, eds., The Conservation of Panel Paintings, Research Agenda, 2014–2020 (The Hague: NWO in association with Rijksmuseum, 2014).
4. Jonathan Ashley-Smith, Andreas Burmester, and Melanie Eibl, eds., Climate for Collections—Standards and Uncertainties (London: Archetype in association with Doerner Institut, 2013), 311–24.
5. Ibid., 257–70.
6. Ibid., 299–310.
7. Ibid., 271–82.
8. Stina Ekelund, Paul van Duin et al., "Climate4Wood," in Austin Nevin, Malgorzata Sawicki, and Kate Seymour, Heritage Wood: Research and Conservation in the 21st Century (Paris: ICOM-CC, forthcoming).