Environmental monitoring and control

Soon after the National Gallery of Victoria was founded in 1861, the Trustees implemented measures to monitor the gallery environment and collections which were then located in Swanston Street at the current State Library of Victoria site. In 1869 the NGV installed several thermometers around the galleries, and attendants were required “to read the thermometer three times a day and make return of the same monthly.” Building improvements were also implemented, including adding hessian filters to the air ducts, and painting out skylights and using blinds to reduce visible and ultraviolet (UV) light levels.

Eugene von Guérard (1811-1901) is best known for his landscape painting, but he also served as a conservator at the NGV. He was aware of the impact of environmental fluctuations and tracked the temperature (T) and relative humidity (RH) in the galleries, making logs of conditions and object response to changes.

By the 20th century, hygrothermographsAn instrument that records both relative humidity and temperature changes over time. could automatically record RH and T on a paper chart fixed to a cylinder rotating at a set rate driven by clockwork or batteries. This offered more detail than regular checking of RH and T. In the 1980s two centuries after von Guérard recorded his first observations the condition of the Collection continued to be monitored through detailed documentation and specialised research.

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The building fabric can play an important role in buffering changes in temperature and relative humidity. Design features of the NGV International building ensure a stable environment, particularly in gallery spaces. The bluestone walls and floors and the building’s closed floor plan provide thermal mass and its small number of windows reduces heat loss and gain. Additionally, limited direct sunlight enters the building, mainly from the skylight over Federation Court through summer. The building is orientated facing the east north-east and with a garden to the west, which contributes to its stable environment.

NGV Australia is integrated into Federation Square, an iconic complex which sits close to the Yarra River. Being a modern building, its buffering relies on a modular system of cladding made of sandstone, zinc and glass mounted on a structural frame. The building has large windows in areas and is subject to more temperature and humidity fluctuations, particularly in areas with windows facing north-east.

Across both NGV buildings, the environment is controlled through each building’s mechanical Heating, Ventilation and Air Conditioning (HVAC) system, which is programmed into the building automation system (BAS) and managed by the Assets and Facilities department. The temperature and RH ranges in which the HVAC system operates take into consideration safe environmental condition for the vast majority of collection and loan items, according to international museum standards, as well as staff and visitor comfort and safety compliance (for example fresh air intake).

Data can be readily retrieved through the BASBuilding Automation System. There are times when more specific readings may be required. For example when NGV conservators wish to know more about the conditions in specific areas or even individual storage units or showcases housing works more sensitive to environmental changes than most. Also, when artworks are borrowed for specific exhibitions, data may need to be sent to external stakeholders. Conservators may also wish to track the conditions around particularly sensitive collection items which travel to other venues regionally, interstate or overseas.

In such cases, NGV Conservation use Wi-Fi enabled data loggers to monitor the temperature and RH in these environments. These are small, unobtrusive electronic instruments which record long-term temperature and RH conditions using inbuilt sensors. The Wi-Fi connectivity allows conservators ready access to the data and can notify of any breaches via email or SMS. Charts can be viewed and reports generated through the software on any PC or mobile device.

Environmental monitoring instruments used today

NGV has an active loans program to local, interstate and international institutions. As a part of the program, NGV Conservation offers support and equipment. To provide easily accessible climate information NGV lends data loggers to institutions where access to continuous climate readings is limited. By connecting the data loggers up to the institution’s Wi-Fi network, NGV staff are able to remotely monitor the environmental conditions of the loan work.

For artworks made up of highly sensitive materials or which have been acclimatised to environmental conditions outside our norms, specific control measures are needed to ensure these pieces are not exposed to environmental shock which may result in irreversible change or damage. NGV conservators can manage these ‘at-risk’ works by creating micro-environments, or microclimates, through either active or passive control measures.

Active systems require equipment to modify the air conditions within a case or storage unit, independently of the external conditions. Active systems are used at the NGV for special collections. For example, archaeological bronzes are kept at a low 35% RH to slow corrosion rates, while weeping glass – glass with an inherent chemical instability at manufacture that results in salts being pulled to the surface by moisture in the air – is stored at a constant RH of 42% to slow this migration process. Special storage cabinets with designated air conditioning units (Miniclimate machines) have been fitted to maintain microclimate conditions.

Passive systems involve the introduction of a desiccant (drying) or adsorbent material which stabilises and maintains set moisture levels within a sealed enclosure. Examples used at the NGV include Artsorb™ and ProSorb™ in either pellet or sheet form. For three dimensional works cassettes of pellets can be inserted in hidden compartments within sealed showcases. For two dimensional paintings, works on paper or photographs, adsorbent sheets can be placed behind an artwork, creating a dedicated environment between the front glazing and rear, non-permeable backing board.

miniClima EBC11 (miniClima Schönbauer GmbH) humidity control unit maintaining low humidity for a weeping glass storage cabinet

Light is essential for the display and viewing of the NGVs diverse collections. However, light can also be damaging to artwork, therefore it is essential for conservators to manage and monitor light exposure. For display, conservators consider three light components: UV and visible light, and infrared (IR) radiation. Visible light refers to the wavelength range of light humans can see (~400-700 nm) and outside these parameters is UV light (700 nm).

These components affect a range of materials in different ways. For example, UV and visible light can cause colour change and fading of dyes and pigments in textiles, leather, wood, paper, and paintings. UV light can cause physical or chemical changes such as yellowing, weakening and embrittlement of organic materials and plastics, while IR radiation can contribute to thermal damage of artworks. Unfortunately, damage caused by light is accumulative and irreversible.

Conservators’ first strategy in protecting the NGVs collection from light is to eliminate UV and IR where possible. The NGV uses filters on windows, display cases and glazing, and use specialised lighting design to illuminate our galleries. The amount of light shone on an artwork is measured and tracked to ensure optimal visibility in conjunction with safe levels of exposure. Displays of light-sensitive artworks are regularly rotated to minimise overall exposure and artworks are methodically assessed for signs of light damage or change by conservators.

The NGV conservation department runs a program to test new materials proposed for use in display or storage environments. To be suitable for use in close proximity to art, these materials must be free of harmful volatile gases that can accelerate degradation of artworks.

Analytical tests are used to determine if a material contains specific components known to have adverse effect on artefacts. Fourier-transform infrared spectroscopy (FTIR) is used to identify organic components while X-ray fluorescence (XRF) is used for elemental analysis, and together they help characterise an unknown material.

The program includes simple qualitative tests for volatile components which have been identified as damaging to artworks. Each test is capable of detecting one specific agent, and most. For example, the Beilstein test is a flame test that can indicate the presence of chlorine which can cause deterioration of many materials including copper, iron and silver. Tests for sulphur (which causes tarnishing of silver and copper corrosion) and acidic vapours (which can cause corrosion of copper and lead alloys and attack calcium-based objects, paper, photograph, and plastics) are also conducted, as is the Oddy test, a 28-day procedure for non-specific accelerated corrosion testing.

D. Thickett and L. R. Lee 2004. The Selection of Materials for the Storage or Display of Museum Objects. The British Museum Occasional Paper No 111, revised edition. London: The British Museum.

J. Tetreault 1999. Coatings for Display and Storage in Museums. CCI Technical Bulletin 21. Ottawa: Canadian Conservation Institute.