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Window glass is one of the most vulnerable elements of a historic building. As demands are made on glazing to improve thermal comfort, this element of historic fabric is under threat of replacement with modern equivalents. Part of the problem in undertaking a survey of historic windows is that it is not always possible by traditional visual assessments to accurately date window panes, and hence identify which panes are historic and which are modern.
The use of portable X-ray fluorescence to determine the provenance and age of glass by trace element analysis has allowed for a scientific approach to historic building surveys. By using this technique, a number of buildings in Scotland have been assessed and this has provided a valuable insight not only in to which historic glass panes remain, but can also give information in to how the buildings have been managed over time.
Utilising this method, it can been shown that the Abbot's House at Arbroath Abbey, an ancient monument in state care, was completely re-glazed in one event in the early 20th century. Traquair House, a private property, appears to have replaced individual panes when necessary, for instance after breakage, leaving windows with panes of glass of varying ages and types. Newhailes, in the custodianship of the National Trust for Scotland, is a large building easily accessible to the public. Its upper floor window panes are largely historic, whilst ground floor panes appear new, indicating that vandalism and breakage have altered the historic character of parts of this building.