Context 143 - March 2016

C O N T E X T 1 4 3 : M A R C H 2 0 1 6 35 JOHN FIDLER Conserving terracotta For all the 19th-century claims about its durability and self-cleaning nature, terracotta is little understood as a material and experience in its conservation is limited. I blame it all on the loveable Dennis Moffat (d2010), bless him. My 36-year love affair with terracotta and faience started with a plaintive call from the front desk at County Hall, where I was hiding out in the attic offices of the GLC’s Historic Buildings Division. In a desperate last move for a salesman out of ideas, and luck, Moffat was traipsing the capital’s streets looking for Edwardian piles with glazed brick courtyards: did we want to buy any replacements? If not, then one of the last great factories producing architectural ceramics would close.The rest, as they say, is history. Since just before and after this event, circa 1980, the two main English manufacturers of terracotta have seen their prospects plummet then soar on more than one occasion. Such is the tenuous grip on commercial success for dedicated craftspeople in an uncaring fiscal environ- ment. Receivers, accountants, banks and commodity brokers have stripped them bare of diversified product ranges (which used to protect them from economic downturns in the construction sector). Famines and feasts follow hard on each other’s heels: with a currently buoyant refurbishment market, continuing overseas demand, and resurrected new-build interests all coming at once, the small-and-medium-sized businesses are now stretched almost to capacity. All power to their elbows. Before recent contributions to Historic England’s epic two-volume blockbuster on the subject1, I last wrote an overview of terracotta conservation issues, ‘Fragile remains’2 , some 22 years ago. Sadly, the basic tenet of that paper remains valid today: terracotta and its associ- ated construction systems remain the least understood of any historic building material. On this score, wheels are constantly being reinvented – witness my former English Heritage colleague, historian Anna Keay (now aTV star and director of the LandmarkTrust), recently poring over a boffin’s microscope on the box to discover the long lost secret recipe of Mrs Coade’s ‘stone’.This ‘myth’ of unknown constituents I put down to blissful ignorance or clever marketing by Alison Kelly for her 1990 book3: the GLC and others carried out scientific analysis of the material back in the 1950s, and potters throughout history have known about and used grog (previously fired clay) to stabilise their products. Knowledge gaps are so widespread that it is hardly surprising that damage has been caused by well-meant but inappropriate cleaning and other remedial treat- ments. Here, then, are a few salient issues to keep in mind. General contractors sometimes try to financially squeeze the terracotta-fixing subcontractors and material makers by claiming that new blocks do not match the old because they are warped. But on most jobs that I have seen, the historic material (remember, shrunk down from 5–13 per cent of its original moulded size) has a very wide range of tolerances for squareness, flatness and so on because of problematic drying conditions or firing variations in downdraft kilns. These deformities need to be measured and the tolerances specified to ensure a match within a defined range. Few self-coloured clays are now available, so the manufacturers invariably produce a neutral off-white/ grey body from selectedWest Country clays and spray it with a slip-stain (engobe) finish that vitrifies in the kiln to become an integral coloured fireskin.The colour, therefore, is only skin deep. A common misconception among specifiers is that terracotta colours are constant for any particular job.This was not the case, nor could it ever be. Colour variations always occurred,within certain limits, depending on the type of kiln used, firing times References 1 Henry, A, McCaig, I, Willett, C, Godfraind, S, and Stewart, J (eds) (2015), ‘Earth, brick and terracotta’,Volume B, English Heritage Practical Building Conservation Series, Ashgate, Farnham 2 Fidler, J (1996) ‘Fragile remains: an international review of conservation problems in the decay and treatment of architectural terracotta and faience’, in Fidler, J andTeutonico, J-M (eds.) Architectural Ceramics: their history, manufacture and conservation (a joint symposium of English Heritage and the UK Institute for Conservation, 22–25 September 1994) , James and James (Science) Publishers, London 3 Kelly, A, (1990), Mrs Coade’s Stone , Self- publishing Association, Upton-upon-Severn The variegated colour caused by glaze-run on Burmantoft’s terracotta at the Midland Hotel, Manchester (Photo: Jonathan Taylor)