The Building Conservation Directory 2023

I N T E R I O R S 5 161 C AT H E D R A L C O M M U N I C AT I O N S T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 3 | C E L E B R AT I N G 3 0 Y E A R S 3D SCANNING AND REPLICATION Most Victorian and Edwardian tile schemes will have seen some repairs since they were made, and the supply of matching tiles from stock is now often impossible. As a result new tiles have to be made to match the originals where damage and losses have occurred. Craven Dunnill & Co Ltd, a tile maker in Ironbridge which this year is celebrating its 150th anniversary, has adopted 3D scanning for the preparation of moulds. For conservation work this has several significant advantages over conventional mould making. Firstly, the scanner’s laser penetrates the glaze to record the form of the ‘biscuit’ – the underlying clay body. Because the liquid glaze pools in the recesses, the form of the biscuit is very difficult to gauge from the surface, and mould impressions taken from the surface of a glazed tile can only be used as a guide to the form of the original unglazed biscuit. Secondly, scanning is non-destructive. Before the advent of scanning, Craven Dunnill Jackfield’s conservators would have to physically remove samples of original tiles from the site for copying by a highly skilled craftsperson and colour matching. In the case of a glazed tile, the only way to establish the exact form of the original biscuit was to carefully remove the glaze using hand tools, completely destroying the tile in the process. Thirdly, in the absence of a digital model, any changes that were needed for the creation of a new mould – such as the construction of an oversize model to allow for shrinkage – had to be judged by eye. Each step relied on the skills of the artist or craftsperson and created room for error. Digitising the process does not remove the need for highly skilled craftspeople, but it reduces uncertainty at every stage. After scanning on-site the digital model is checked and adjusted as necessary, for example to accommodate any defects or damage in the original tile. This model is then used with CNC machining to make the die or plaster mould, and the carving is then refined by hand by the artist or craftsperson. As well as being instrumental to the quality of any carving or modelling, the role of craftspeople remains crucial for the identification of the appropriate clays, glazes and firing processes required to match the colours and form of the original, and to ensure compatibility. The digital process also has the advantage that computer-aided design is now part of Craven Dunnill Jackfield’s design and estimating process. CAD drawings and 3D models can be used to help the whole conservation team visualise the outcome before committing to physical models. Layouts for wall and floor tile are also designed using 3D modelling software, allowing for tiles to be automatically counted, and any layout issues resolved before committing resources to a project. Recommended Reading Practical Building Conservation: Earth, Brick & Terracotta, Ashgate & Historic England, 2015 Hans van Lemmen, 5,000 Years of Tiles, The British Museum, London 2013 Adam Watrobski, ‘Encaustic Tiles at the Palace of Westminster’, The Building Conservation Directory 2017 www. buildingconservation.com/articles/ encaustic-tiles/encaustic-tiles.htm This article was prepared by the editor, Jonathan Taylor, whose MSc dissertation was on the conservation of Victorian terracotta. Information on the development of laser scanning was contributed by Craven Dunnill Jackfield’s R&D team. A further article on the repair of tiles and mosaics will be published in the 2023 edition of Historic Churches . One of Craven Dunnill Jackfield’s technicians scanning the tiles on a curved bar front to create a 3D model: variations in the depth of the translucent glaze can be seen from the darker areas where the fluid glaze pooled. (Photo: Craven Dunnill Jackfield)