An article recently published in the prestigious scientific journal Geoheritage has employed artificial intelligence techniques to detect and catalogue UNESCO World Heritage buildings and monuments that have slate roofs. This work (A Review of History and Architecture of Roofing Slates: Impact on the UNESCO World Heritage List) is authored by Víctor Cárdenes, Celia Campa, and Luis Pando, all of whom are professors in the Department of Geology at the University of Oviedo. The article explains, on the one hand, the cultural value of slate roofs as an essential component of the historical and architectural heritage of humanity and, on the other hand, the development of digital techniques for identifying roofing materials.
UNESCO is the United Nations Educational, Scientific and Cultural Organization. One of its most iconic programs is the World Heritage List, which consists of a register of places and buildings with special significance for humanity. This list recognizes sites in three categories—cultural, natural, and mixed—and currently includes more than 1,200 listed sites. Places included on this list enjoy the highest level of cultural and historical recognition worldwide. Slate is the most widely used natural rock for roofing and coverings since Roman times, which is why it is not uncommon to find it in buildings listed by UNESCO. From the Late Middle Ages onwards, between the 11th and 15th centuries, its use became widespread in the great European cathedrals and castles, which display imposing slate roofs. In Spain, the Monastery of El Escorial stands out; it was built in the second half of the 16th century and features a bright grey slate roof sourced from Bernardos, in Segovia. Later, during the 20th century, the exhaustion of historic European quarries and the need for high-quality slate for the maintenance and restoration of historical heritage drove the emergence of slate from Galicia and Castile and León in the European market. Today, Spanish slate indisputably dominates the global market, with its presence in buildings and monuments on the UNESCO World Heritage List serving as one of its strongest credentials.
The other novel aspect of this work is the use of artificial intelligence techniques to identify the materials from which roofs are made. Based on images available on the UNESCO website, it has been possible to distinguish slate roofs from those made of other materials. This makes it possible to determine different types of roofing and, where appropriate, to detect fake or imitation slates. Imitation slates are tiles made of plastic and asphalt-based materials with colors, textures, and dimensions similar to those of genuine slate. This type of material has achieved some market penetration in countries such as the United States, where it is sold as a cost-effective solution, despite having much lower durability than real slate, along with a significantly higher environmental impact. In this study, fake slates were detected at several sites included on the World Heritage List, which is particularly concerning, as these sites represent the highest level of cultural recognition worldwide.
In summary, this work highlights the great historical value of slate roofs, as demonstrated by their relevance on the UNESCO World Heritage List. However, the fact that imitation slates have been found on buildings included on the list is worrying, as they distort the historical character of the sites and provide a misleading representation to the public.
Víctor Cárdenes Van den Eynde
Profesor Titular de Petrología y Geoquímica, Departamento de Geología, Universidad de Oviedo
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