C O N T E X T 1 1 6 : S E P T E M B E R 2 0 1 0 5 Periodically On this occasion your reviewer has chosen to concentrate on two substantial periodicals and the future prospects for a third. The latest issue of the Journal of Architectural Conservation (Vol 16, No 2) provides the usual invaluable mix of repair techniques and evaluation methods. In the first paper, the consulting engineer Michael Beare discusses his appraisal of the principal facades of Selfridges department store, Oxford Street, London. Designed with input from Daniel Burnham of Chicago in a visually uniform, classical beaux arts style, the store was built in eight phases between 1909 and 1928. This resulted in significantly different constructional forms being adopted which now pose different challenges for maintaining the fabric. The author discusses the use of cathodic protection systems on the steel framework. He demonstrates the potential for the principles adopted in this project to be applied to other steel frames located behind masonry constructions elsewhere in the world. Other protective treatments, this time for the sugaring of marble, are set out by Elena Charola, Silvia Centeno and Kyle Normandin in respect of their work on the NewYork Public Library. The marble was found to be in a fairly good state of conservation apart from the more exposed elements, such as quoins and the many delicately carved decorative elements. The authors explain the treatment developed for areas that showed significant sugaring. Laboratory examinations and analyses were carried out, and preliminary tests were made with silicate ester- based consolidants. As these did not perform well in tests, an approach using inorganic materials was developed. This used saturation spray applications of an ammonium oxalate solution to increase the cohesion of the marble and reduce the intensive sugaring. A shelter coat followed, based on Type S hydrated dolomitic lime to protect these surfaces further, while being fully compatible with them. The authors conclude that one of the advantages of the oxalate treatment is that it is closely related to the inorganic nature of the stone substrate, in comparison to silicate ester treatments. Over a century had elapsed without a major intervention to the library, aside from a comprehensive cleaning of the facade in 1989. If present conditions persist and air pollution continues to decrease, 25 to 50 years may elapse before more ‘extraordinary maintenance’ will be required. The journal regularly provides insights into the conservation of innovative modern construction materials that are coming to be seen as historic. One such is Vitrolite, used in the early part of the 20th century but no longer manufactured.The paper by Fiona Hudd examines the history and importance of the glass, and practical issues surrounding its conservation today. Hudd uses case studies to demonstrate the specific problems and solutions. Case studies include the well-known Grade II* listed former Daily Express building in Fleet Street by Ellis, Clarke, Atkinson and Sir OwenWilliams (1932). These illustrate some of the issues at the heart of the debate surrounding the conservation of 20th-century historic buildings. The author points out that the architecture of the early 20th century is vulnerable in two ways. The fabric of buildings often suffers from the cheapness of the construction, in-built design faults and lack of maintenance. But it is also vulnerable to change from upgrading and renovation work. Lack of double glazing or insulation in external walls is increasingly considered unacceptable in 20th-century buildings, and the consequences of experimental forms of construction such as reinforced concrete frames or flat roofs are seen as defects which must be rectified before a building can remain in active use. If the perception is that past ‘imperfections’ must be brought up to date, the unique historic value may be lost. Hudd concludes that if an original fabric such as Vitrolite has inherent value, and its particular visual qualities and resilience to weathering are recognised and properly cared for, it could continue to function as originally designed for the foreseeable future. Replacement of an entire Vitrolite facade with an alternative, modern material could be seen to undermine its heritage value. It has yet to be demonstrated that there is a comparable modern material which can achieve the particular blend of depth of colour, reflectance and surface finish which Vitrolite and similar glasses provided. The value of these glasses lies not only in their aesthetic appeal, but also in their evidential and historical associations. They tell the story of glass manufacture in Britain and its links with America in the 1920s and 1930s, and of architectural innovation and development in British architecture. The ruined city of Petra in Jordan is internationally famous. It had decayed only slowly in the 2,000 years of its existence. This changed with the emergence of mass tourism in the 20th century. The city now sees 4,000 visitors a day, with all the attendant physical erosion and increases in humidity, particularly at its two most celebrated structures, al-Khazneh and the Urn Tombs. Thomas Paradise, professor of geosciences and geography at the
RkJQdWJsaXNoZXIy MjgyMjA=