Photo-based decay mapping of replaced stone blocks on the boundary wall of Worcester College, Oxford
Published:January 01, 2007
M. J. Thornbush, H. A. Viles, 2007. "Photo-based decay mapping of replaced stone blocks on the boundary wall of Worcester College, Oxford", Building Stone Decay: From Diagnosis to Conservation, R. Přikryl, B. J. Smith
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In this study on the boundary wall of Worcester College, Oxford, the decay mapping in Adobe Photoshop (DMAP) approach is introduced to test the use of simple daylight photographs in the long-term monitoring of stone decay. This is conducted primarily through measured changes in surface brightness and roughness based on close-up photographic images of walls. The Magic Wand Tool was applied to greyscale images in Lab Color Mode to select proportions of pixels with a lightness (L) value of 77%. This paper shows the effectiveness of the calibration procedure used to validate lightness between surveys so that cross-temporal comparisons have a greater validity. It also outlines and discusses errors associated with the method as well as its limitations. The DMAP approach proves to be particularly useful when applied to long-term monitoring exceeding 5 years of survey.
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Building Stone Decay: From Diagnosis to Conservation
Stone buildings and monuments from the cultural centres of many of the world's urban areas. Frequently these areas are prone to high levels of atmospheric pollution that promote a variety of aggressive stone decay processes. Because of this, stone decay is now widely recognized as a severe threat to much of our cultural heritage. If this threat is to be successfully addressed it is essential that the symptoms of decay are clearly identified, that appropriate stone properties are accurately characterized and that decay processes are precisely identified. It is undoubtedly the case that successful conservation has to be underpinned by a comprehensive understanding of the causes of decay and the factors that control them. The accomplishment of these demanding goals requires an interdisciplinary approach based on co-operation between geologists, environmental scientists, chemists, material scientists, civil engineers, restorers and architects. In pursuit of this collaboration, this volume aims to strengthen the knowledge base dealing with the causes, consequences, prevention and solution of stone decay problems.