C O N T E X T 1 2 4 : M A Y 2 0 1 2 5 Periodically When you see a window, what do you see – the frame or the glass? The answer should be both, but many practitioners spend so much time trying to ensure the conservation or replication of the correct framing that the importance, and historic and visual significance of the glass can be overlooked. As a fragile material it is particularly at risk of loss and incorrect replacement. The latest edition of the Journal of Architectural Conservation (Vol 18, No 1, March 2012) has a very informative paper by David Dungworth of English Heritage’s archaeological conservation and technology team on the characteristics of glass. It explains the results of Dungworth’s research into the chemical composition of window glass from different eras from the 14th century onward, particularly from the 17th century. He shows how a handheld, portable X-ray fluorescence spectrometer has the potential to analyse glass panes in situ, identifying historic glass of different periods without damaging it. If the optical characteristics of historic glass are correlated with its chemical composition, it becomes possible to assess its age and significance more accurately. This should help highlight the need to conserve it and protect it during refurbishment. The second paper, by Dante Vanoli of Purcell Miller Tritton Architects, presents an exemplary case study on the conservation and re-servicing of the Arab Hall at Leighton House, in Holland Park, London (listed Grade II*), undertaken between 2008 and 2010. The house was built over a 30-year period from 1865 for Lord Frederic Leighton (1830–96), a prolific painter and sculptor, noted aesthete and president of the Royal Academy. He used his personal collection of rare Islamic tiles and tesserae as the inspiration to create the Arab Hall as the decorative centrepiece of his house and studio. As the house remained open to the public, the conservation of these delicate materials had to take into account the requirements of continued public access. The availability of a comprehensive collection of primary documentary sources ensured that the refurbishment would conserve the existing fabric and where necessary reinstate Leighton’s original decorative conception. Some of the conservation work is illustrated in colour. The third paper demonstrates what could be called technology transfer – adopting technologies not previously associated with conservation for its benefit. Poul Larsen has been using a dielectric probe adapted from soil science to monitor the movement of moisture in brick masonry walls of Danish historic buildings over a five-year period. He explains how the probe can be adapted and calibrated to assist those considering similar investigations. The drawback appears to be the timescale needed to collect sufficient data to form an understanding of the processes at work. This may explain why so few similar studies are being undertaken in the UK or elsewhere. Larsen’s results illustrate both the long timescales needed for damp walls to dry out and the role salts play in that process. The benefits or otherwise of using limewater as a consolidant of limestones and plasters (introducing large volumes of water into historic fabric) and the difficulty in getting calcium carbonate to penetrate the stone sufficiently seems to lead to something of a polarisation of opinion among practitioners. One solution to these concerns appears to be the use of nano-lime, as this retains the inherent compatibility of limewater. As a consolidation technique it is gaining increasing acceptance, but its practical evaluation has not so far been well documented. The paper by Elizabeth Hirst and Paul D’Armada is therefore both valuable and a timely introduction to the material. It summarises the research on its use in consolidating important early-14th century wall paintings at the Grade I listed All Saints’ Church, Little Kimble, Buckinghamshire. The final paper, by Isobel Griffin and JimTate, extemporises on the heritage significance of defensive structures (also explored in Context, November 2011). The authors set out their analysis and proposals for its conservation of a second world war concrete air raid shelter at a former Royal Naval Air Station at East Stanton, East Lothian. The site, the National Museum of Flight since 1975, has been described as ‘the best preserved collection of airfield technical site buildings on probably the most complete second world war temporary airfield in Britain’. It was scheduled as an ancient monument in 1991. The shelter is not a particular rarity in itself, but it contributes significantly to the integrity and authenticity of the overall airfield. Conserving structures originally intended to be robust but with a short life expectancy is complicated, but clearly justified by their survival. The authors explain their detailed research to establish the mechanisms of the deterioration of this partly buried structure and the conservation options, guided by the parameters of the new British Standard for concrete repair, BS EN 1504. A wide range of engineering history subjects is covered by The Institution of Civil Engineers Proceedings on Engineering History and Heritage. Volume 165, issue EH1 (February 2012) is no exception. The edition carries four papers, two of which will be of particular interest to UK readers.
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