MUSEUM MICROCLIMATES
Introduction by Tim Padfield
The articles collected in this volume give a snapshot of current opinion and research in the preservation of artifacts through manipulation of their environment. There is little about exotic environments such as oxygen free enclosure or cold storage but abundant advice and information about reducing fluctuations of temperature and relative humidity in spaces that are within the environment for human comfort but not in accord with current standards for the museum environment.
Several authors concentrate on buffering the microclimates in small enclosures, to make the relative humidity, at least, independent of the ambient air [Thickett 245, Shiner 267, Watts 253, Toledo 261, Hackney 229]. It is far more difficult to prevent heat exchange with showcases so there are several articles about the influence of temperature change and temperature gradient on the atmosphere within small enclosures [Richard 237] and its consequences [Ligterink 27, Mecklenburg 19].
Calming the unruly climate of historic buildings is a challenge that is being met in several ways. One author [Larsen 167] presents case histories of architectural modifications, such as glass partitions, as a practical way of reconciling public comfort with preservation of salt contaminated wall paintings. A detailed examination of the climate in a private house museum describes it as acceptable though not ideal [Maekawa 99]. A more systematic and abstract attempt to define the allowable climate fluctuations in historic buildings [Bratasz 129] asserts that future fluctuations in a particular building should be limited to less than past fluctuations by a statistically defined amount, in preference to imposing a standardised climate specification that takes no account of the past climate in that particular building. In one extreme case, the authors advocate making an open pavilion into a closed room to reduce winter damage [Lithgow 175].
The strain of ameliorating the damage done by a bad climate is particularly evident in the tropics. Passive enclosure is surprisingly effective in reducing the extremes of relative humidity which vastly accelerate biological activity [Toledo 261]. Simple measures to ventilate during naturally dry periods of the day can also help to reduce damage [Broecke 213].
Scepticism over the validity of strict universal standards is evident in many contributions [Erhardt 11, Ntanos 91, Padfield/Larsen 191, Bratasz 129]. Risk analysis is hailed as the better way to decide what needs to be done urgently to preserve artifacts in a particular environment [Fry 107, Brokerhof 115]. Risk analysis depends on an accurate description of the connection between the environment and the deterioration of artifacts. There is still rather little scientifically exact and quantitative data about this. One article compares the preservative effect on paper of deacidification and of cooling [Balazic 39]. There is also an attempt directly to measure the deterioration of some of the materials of historic artifacts by plating them on quartz crystals and measuring weight change on exposure, as revealed by vibration frequency change [Odlyha 73]. Egg tempera paint is multi-sensitive to environmental influences but lead is fairly specifically sensitive to organic acids [Costa 63].
Enclosure of artifacts in showcases and frames reduces access to air pollutants and dust, while allowing the accumulation of corrosive gases from the materials of the interior of the enclosure and the enclosed artifacts [Ryhl-Svendsen 221]. There are contributions to the analysis of atmospheric pollution, and there is a considerable interest in dust, its composition and its pattern of deposition, particularly in environments where enclosure is not practical, such as in historic house libraries [Lloyd 135].
There are two articles about techniques for measuring air quality [Costa 61, Schieweck 67]. There are contributions about how to use these measurements to define the aggressiveness of the environment [Reilly 121]. An infra red technique is described which promises to give a good indication of the state of preservation of paper [Strlic 81] but until parallel environmental measurements have been made one cannot correlate environmental parameters with measured damage.
One of the matters curiously absent from the risk analysis articles is the risk that the environmental records that underpin risk analysis fail to survive in the digital age of rapid obsolescence of computer programs and storage formats and the uncertain durability of storage materials [Padfield 157].
Another matter that risk analysers seem to accept as beyond their power to influence is the architecture of the museum. In the Royal Ontario Museum many showcases have piped air to isolate them from the exhibition room relative humidity [Coxon 277], even in the newest extension to the museum. The physics of designing for a naturally good climate without air conditioning is laid out in one article [Padfield/ Larsen 191] and the experience of using a purpose built store is described in another [Rasmussen 207]. Windows are a source of glare and of uncontrolled light but they also provide the most energy efficient lighting and can greatly reduce heating caused by artificial lighting [Huber 199].
Remarkably, photochemical deterioration attracts very little research nowadays. In this volume there is only one review article about museum lighting [Druzik 51]. The biological articles are limited to a review of the effect of temperature and relative humidity on the life of insects [Child 57] and a calculation method for assessing the risk of mould growth within the outer walls of buildings [Krus 185].
To summarise this volume, there is much about making artificial microenvironments, mainly to control relative humidity. The economic advantages of using risk analysis to put climate control in its proper place among the agents of destruction continues to be a focus of attention. The lack of scientific evidence of decay rates to back up stringent environmental standards continues to embarrass the preventive conservator. The disregard for microclimate shown by museum architects continues to be accepted humbly by conservators, in spite of evidence that pleasant buildings can be constructed with far greater natural stability in climate than is shown by the current crop of dramatically sculptural museum buildings.
All the articles in this volume are copyright the authors but have a creative commons licence, making them free to download and free to distribute in any way, as long as you acknowledge the authors, you do not change the articles and you do not profit from reproducing them.
A paper version of the volume can be bought from the bookshop of the National Museum of Denmark