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Opinion: Jane Henderson - Curators and Conservators need to be careful that they don't turn recommendations on environmental standards into rigid rules.

Henderson, Jane 1996. Opinion: Jane Henderson - Curators and Conservators need to be careful that they don't turn recommendations on environmental standards into rigid rules. Museum Practice

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The theory goes: control your light to 50 lux (200 for less sensitive materials), reduce your ultraviolet light to less than 75 microwatts per lumen and confine the humidity to the magical band of 55% +/- 5% RH and your collections will be impregnable. These numbers will be familiar as the cornerstone of all that is good and true in environmental control. If you have a copy of Garry Thomson's The Museum Environment (second edition), let it open on any page. Unless you sat an exam on the museum environment it will fall open at the extremely useful appendix, Summary of Specifications. You will soon realise that this summary of the book's main recommendations can be photocopied and handed out to architects and designers without you having to read any further. Sadly this is not uncommon and explains why the standards are well known but the reasons for their existence are not. Lighting standards Lighting is a subject which can unite curator, designer, visitor and marketing manager in an unholy alliance against the conservators. The conservator has, in the pursuit of the 50-200 lux dream ticket, switched off almost every light in the gallery and confined most of the collection to the store. So where does the 50-200 rule come from? The answer is, of course, Garry Thomson. Any light exposure will fade objects so there is no safe limit. Thomson's approach was that with well-organised lighting it was possible to create good viewing conditions and minimise damage to the collections. The 50 lux figure was based on a combination of the minimum light necessary to see an object and on pre-1960s light levels in galleries. As for the 200 lux level, researchers found this was visitors' preferred level providing the light source was of good quality. Proposed as compromises, these fast became rules. Light damage is a result of both intensity and `time of exposure (millions of lux hours or Mlx). It can be rationed: if, say, an object is exposed to 50 lux for a year, the damage done is equivalent to six months' exposure at 100 lux. I suspect future loan conditions for light-sensitive material will specify a total exposure rather than a top limit. Ultraviolet Given that exposure to ultraviolet light is damaging and that it is rarely of any benefit to the viewer, the ideal limit is none. Thomson's work, however, is rooted in practicalities. Ordinary light bulbs have a comparatively low ultraviolet emission and were fairly common in museums when The Museum Environment was first written. To suggest ultraviolet levels equivalent to, or less than, those emitted by a tungsten lamp seemed practical. As lighting fashion has changed and better ultraviolet filters have been developed, some institutions have set lower limits. Humidity Humidity levels are often the hardest targets to achieve. Although Thomson recommends 50% or 55% +/- 5% RH, some humidity control fetishists demand control of +/-3% or even 1% RH. What is the ideal humidity level? For moisture-absorbing material this was suggested to be 55% RH, although for other materials other recommendations are made. Thomson looked for a minimum fluctuation possible using the available technology and came up with +/- 5%. Despite more recent work on how humidity fluctuations can cause damage, an ideal level remains elusive. After extensive and thorough research, Erhardt and Mecklenburg came to the conclusion: `There is no one ideal relative humidity for museums… Extreme values and rapid or large changes in RH should be avoided.' There must be more debate So where does this leave us? Clearly the existing standards were introduced with practicality and accessibility in mind. Yet their implementation has not always matched that ambition. On the subject of loan conditions, Jonathan Ashley-Smith in his talk. Let's Be Honest, put into words what many of us suspect: `Borrowers and lenders do not tell it like it is. At best they are deliberately lying… or, at worst, they have no idea what they are talking about.' Unless Thomson's recommendations are applied carefully, they will not always be helpful. For some collections they will not even be safe. It is time to extend the debate about environmental standards, particularly in the case of loans between museums. What's needed is honest and informed discussion on what really matters rather than an unquestioning application of a set of `magic' numbers. Jane Henderson is Conservation Manager, Council of Museums in Wales. This article was first presented as a talk at the 1995 annual general meeting of the Federation of Museums and Art Galleries in Wales

Item Type: Article
Status: Published
Schools: History, Archaeology and Religion
Subjects: A General Works > AM Museums (General). Collectors and collecting (General)
Uncontrolled Keywords: Magic Numbers conservation environmental standards museum Garry Thomson
Publisher: Museums Association
Date of Acceptance: February 1996
Last Modified: 17 Jun 2019 11:00

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