Museum environment issues include temperature, humidity, light, atmospheric pollutants, and dust, which are typically controlled in buildings that contain collections of cultural and scientific significance. These environmental factors are all 'agents of deterioration' that cause damage to objects, as they play a role in deterioration pathways such as oxidation, hydrolysis, cross-linking and chain scission.
Conservators, collection managers and facility managers often work together to control the environments in which cultural heritage is stored, transported, and displayed. As the conservation-restoration profession has developed, various environmental recommendations or guidelines have emerged. The temperature and relative humidity range considered acceptable in any one cultural organisation may vary according to the type of building, the presence and type of air conditioning systems, and the types of collection material present. Many collecting organisations will also expect these conditions to be maintained during transport and when collection objects are on loan to other organisations (as part of a loan agreement).
Published environmental guidelines for museums tend to minimise both extremes and fluctuations of temperature and relative humidity. Increasingly, the benefits of environmental controls for museum collections are balanced against the energy and environmental costs of maintaining relatively tight parameters. Published guidelines now also take a more holistic approach by taking local conditions into account – e.g., that it may not be possible or appropriate for a museum located in the tropics to maintain an environment more typical of temperate regions.
Sustainable energy use
Heritage machinery Maintaining and displaying the functional capability of a mechanical heritage object enables audiences to immerse themselves in the sensory experience of the display, which imparts information about scientific and technological advances and allows people to make personal connections with the machines. Operating heritage machinery also helps to keep physical components in good condition, and provides opportunities for preserving and passing on the customs and knowledge held by communities of practice who work with heritage machines. Much of this is tacit and embodied knowledge that, like riding a bicycle, has to be learnt through physical experience and practice.
Heritage machines mostly run on fossil fuels, though, which means that they rely on environmentally damaging extraction processes, emit greenhouse gases (and other pollutants), and usually leak lubricating oils. This raises the ethical question of whether operating these machines is important enough to justify their environmental impacts, and the practical question of whether the fossil fuels and lubricants they require will continue to be available/affordable for the heritage sector as the extraction, refining and distribution of these materials is reduced and/or eliminated.
Through the development of sustainability policies, heritage machinery collections can employ strategies to ensure that these cultural heritage objects continue to get exposure for generations to come.
Strategies for sustainability policies
Offset emission While the emissions from heritage machines are unavoidable, carbon offsetting is a strategy that counteracts the environmental impact of running the machine as a functional display. Such offsetting strategies include:
Carbon credit purchases: in which cash is exchanged for carbon credits, with each credit equating to one metric tonne of carbon dioxide (CO2) equivalent that has been stored or avoided by a project. In Australia, Climate Active provides guidelines and minimum standards for calculating and auditing offsets. Community partnership projects, in which the institution or collection runs or participates in greenhouse gas abatement activities or projects which are eligible for the issue of carbon credits. An example of such a project is the Sustainable Destination Partnership, in which the Australian Museum is a founding member. Museum environment emission reduction: Is achievable through making changes to the building envelope; such as the use of rainwater tanks, solar panels, grey water tanks, closed loop hydraulic or air pressure systems or planting trees for passive climate control. Emissions sold as a product: in which there is a direct capture of CO2 (DAC) from the site of emission to be resold and recycled into chemicals or fuel. For further reading on the economic viability of emission sale, see the Columbia University 2021 report .
Run sustainable In situations where it is socially, economically and ethically viable to reduce or negate emissions, the following strategies may apply:
Make a replica: The production of a replica, as either a static cut-away display or as a dynamic machine run on cleaner energy, can demonstrate the mechanical principles of the heritage machine; thus reducing the need to run the original heritage object. Leave as static exhibit: By reducing or stopping altogether the machines running time, the cost of maintenance and energy is saved, while the machine can remain in-situ unmodified for the enjoyment of future generations. However, this action requires careful consideration for while all fluids can be drained by the machine for a clean display, some machines will seize without regular lubrication, with a seized machine risking non-functionality in future situations. Modify exhibit setup: Some machines can be turned into closed-loop systems which can reduce the running wastage and resource cost. However, careful consideration must be undertaken as heritage machines were not designed to function in a close loop and such a setup can risk voiding warranties and increasing maintenance costs due to fouling and corrosion. Modify heritage object: This is by far the most drastic strategy, for while machines are adapted or changed to meet functional requirements during their working lives, the intentional modification of heritage objects runs the risk of violating a heritage institution's and or a conservator's code of ethics and best practices. However, without modifications to reduce emissions or resource consumption, some machines may lose their cultural relevance through lack of awareness, appreciation and respect born out of an audience's lack of exposure
Relocation and collaboration Transfer stewardship: through a loan or Memorandum of understanding with an appropriate Special Interest Group (SIG) or association, with the understanding that the item will be returned and or re-donated to the museum after a specific time period. In exchange for transferring stewardship and cost to public organizations and private collections, a museum can commit to providing advice and or training on significance assessments, fund sourcing, conservation & restoration practices & technical skills to maintain object, thus counteracting shortfalls in the Industrial Heritage's volunteer sector Decommission & document: Create a digital archive of associated machinery information, photographs, schematics, oral history recordings, rather than preserving physical objects. +International Special Interest Groups (SIG) for Heritage Machinery conservationNameThe International Committee for the Conservation of the Industrial Heritage (TICCIH)Big Stuff Heritage Scottish Transport & Industry Collections Knowledge Network (STICK)
Museum environments – early examples During the first half of the twentieth century, many organisations and individuals noted parallels between temperature, relative humidity (RH) and the condition of objects in museum collections. Gradually, relative humidity levels between 50% and 60% became preferred, for example after observing that paintings and other collection items from Britain's National Gallery showed no further damage while stored in environmentally stable caves (58% RH) during World War II but began to crack and flake when returned to the National Gallery in London, which did not have air conditioning until 1949. Hence, when air conditioning was introduced, 58% RH was chosen as the target value. A survey conducted by Harold Plenderleith in 1960 found that most museums aimed for or experienced RH values between 50 and 60%.
The Arrhenius equation, first published in 1889, has also been influential in the development of museum environmental recommendations. Broadly, the equation shows that for every 10 °C increase in temperature, the rate of chemical reactions will double.
The Museum Environment Garry Thomson's 1978 publication The Museum Environment was a major influence in the development of environmental guidelines for cultural organisations and the field of preventive conservation. Though critical analysis shows that Thompson did not intend for his recommended parameters for temperature and relative humidity to become 'rules', nevertheless over the subsequent decade 50% ±5 RH and 21 °C / 70 °F ±2 became the default and preferred parameters for the international community. They became a particularly convenient standard for loan agreements.
Material-specific recommendations Research in the 1990s and 2000s lead towards more nuanced environmental recommendations for different classes of objects and materials, based on their sensitivities. There was greater consideration of both the chemical and mechanical effects of temperature and RH.
In 1993 the Image Permanence Institute released The IPI Storage Guide for Acetate Film, written by James Reilly. Based on accelerated ageing tests, this resource showed how lowering the temperature and RH could prolong the useful life of cellulose acetate film.
In the mid-1990s, researchers at the Conservation Analytical Lab of the Smithsonian Institution conducted research to characterise the response of wood, canvas paintings, acrylic paints, photographic emulsions and paper to fluctuations in RH, leading to more specific recommendations for allowable RH fluctuations. For example, their research found that oil and acrylic paints were susceptible to cold temperatures but little affected by RH. However, other elements in 'layered' objects such as paintings may be vulnerable to RH change, such as gesso ground layers underneath the paint, or wooden or canvas substrates. This research also drew attention to the energy costs of tight environmental controls.
Researchers at the Canadian Conservation Institute (CCI) also developed more nuanced guidelines for temperature and RH, categorising materials as low, medium or highly sensitive to specified parameters and specifying critical levels beyond which chemical, biological or physical change would occur. For example, at 50% RH and 20 °C a chemically stable format like black and white photographic negatives on glass is expected to have a useful life of about 300 years, compared to 1500 years at 10% RH and 20 °C. In comparison, chemically unstable materials like magnetic media formats (audio and video cassettes) are expected to have between 10 and 50 years at 50% and 10% RH respectively. A moderately sensitive material might last 150 years in a warm room (25 °C) but 6,000 years at 0 °C. Waxy materials soften above 30°C (an issue for wax-lined paintings); many plastics distort above 60 °C (PET, acrylic, Nylon, ABS). Conversely, below 5 °C many paint materials enter a glassy phase that makes them more susceptible to physical damage.
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