BCD 2019

INTERIORS 5 163 C AT H E D R A L C O MM 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 1 9 SCAGLIOLA RESTORATION MICHAEL KOUMBOUZIS M OST CONSERVATION professionals will have heard of scagliola; some may even know how to pronounce it (with a silent g). But for those who know it really well, craftspeople and professionals alike, this intriguing technique is the undisputed Rolls Royce of interior finishes. It is a method developed in the 17th century for producing exquisite surfaces that replicate rare, extinct marble, or semi-precious stone. It is a highly versatile material that can take many forms: a wall panel, a full size column, a chimneypiece, an ornament, or even shaped into intricate inlays reminiscent of the Florentine sought-after pietra dura table tops. Under the hands of an accomplished scagliolist, the result will not only look but also feel exactly like the imitated marble, albeit a little warmer to the touch. It also develops a patina and a certain softening over the years which adds to its value and interest. Scagliola is a refinement of a process used by the ancient Egyptians, Romans and Greeks. If a city could not afford the expensive white marbles of the time, they would render an inferior one with a white lime-based substance that could be polished as if it were an expensive one like the Pendelikon white marble from Attica. Scagliola is made from plaster of Paris (a pure form of gypsum, principally calcium sulphate) with the addition of earth pigments, crushed minerals and other materials, carefully manipulated to create the desired effect. However, the exact process used by individual craftspeople remains shrouded in secrecy. When working on site, many of the earlier scagliolists would only work behind screens to keep inquisitive eyes at bay and to preserve the aura that surrounded this seemingly magical technique. DETERIORATION MECHANISMS Scagliola has many enemies, the most common one being moisture. Exposure to water and damp will cause staining or efflorescence (a bloom of salt crystals on the surface), resulting in a loss of surface polish while the plaster itself may become soft or powdery. Persistent leaks in the fabric of a building above can etch the surface of the material, making restoration particularly difficult. Another common problem is physical damage caused by impact or movement in the structure or fabric of a building. Impact cracks to the scagliola are dangerous as they break the protective oil layers and open the surface up to moisture. Building movement may be caused by decay and deterioration, mild earthquakes and, particularly in London, WW2 bomb damage, causing cracks and losses to appear on architectural features such as columns which are bound into the structure of a building. However, it is the wear and tear caused by the passage of people which is perhaps the most common reason why scagliola surfaces have badly deteriorated. While it is always best to conserve historic fabric as found, retaining the patina of age, The lapis lazuli scagliola pilasters in the music room before their restoration