6 C O N T E X T 1 7 4 : D E C E M B E R 2 0 2 2 Periodically Association of Preservation Technology Bulletin One of the most important and informative periodicals received by this reviewer is the Association of Preservation Technology Bulletin (Vol LIII, No 1, 2022). The content is at the cutting edge of current heritage management; it never ceases to be illuminating; and it is an essential primer for best practice.While it may not be easily accessible to some Context readers, it is always very well worth seeking out. One great concern in heritage management is the extent to which the presence of concealed historic fabric can be assessed. Owners and occupiers are often reluctant to damage important surface finishes in order to investigate the structures behind, particularly when this may be abortive and present problems of loss of surface fabric and seamless reinstatement. The article by Lucy Midelfort on active infrared thermography as a non-destructive investigative tool to locate evidence of historic fabric is an essential read. The paper demonstrates the use of commonly employed methods in the search for previous or concealed locations for decorative hardware, fasteners and historic structures. But the general principles and techniques involved could be used to great advantage elsewhere. The author shows that the method has helped uncover, not only evidence of past interior furnishings, but the historic treatment of spaces and the implications for their use. Her paper helpfully indicates the limitations of the technique and where these require further investigation to develop a rubric to determine when it will be most useful. Midelfort makes the point that the procedure has been useful on wall substrates but not on plaster. This is likely because many of the potential fill materials have properties closer to plaster than wood, and differentiation using thermography on a plaster substrate is more challenging. Thus more study is required on the efficacy of various heat-delivery methods and the ability to determine fill types without destructive evaluation. The author hopes that the study reported in the paper will prompt ideas about further test applications of the technique and a greater understanding of situations in which active infrared thermography can be used in historic settings. Lauren J DeCenzo and Caroline L Searls write about new alternatives for repairing terracotta exterior walls where the glazing has spalled. Traditional glazed terracotta used for building cladding typically consists of a high-fired bisque with an outer surface of a vitrified glaze. The glaze helps resist water penetration to the overall cladding but when it does deteriorate over time, small areas of the glaze, or the glaze and a thin layer of bisque, may laminate from the body of the terracotta blocks leading to water infiltration, further deterioration and corrosion of any embedded steel anchors. A recurring challenge is the lack of durability from in situ repair coatings. The authors explain the methodology and performance of coatings on both wet and dry substrates, and include a description of the selection or materials, based on industry trends and previous experience; sample conditioning; coating application; and storage. They explain the effects of curing on a continuously wet substrate of polyurethane coatings that had been applied. This will be a useful article, examining the problems and potential solutions where localised terracotta deterioration is encountered and repair is required. Developing an appreciation of appropriate maintenance to modern historic buildings can be a challenge, particularly when users and managers need to be persuaded of its value. The Washington DC Metro is both an important piece of 20th-century infrastructure and architecture of heritage value. Recent inappropriate work identified by the United States Commission on Fine Arts has been described as ‘the sudden painting of the monumental concrete vaults with layers of white paint, […] not an instance of routine maintenance
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