Landscape Dynamics

Did you know that the iconic 13 carved heads that ring the perimeter of the Sheldonian Theatre are the third generation to have sat there watching over passers-by? These heads have been continuously exposed to varying environments, both social and natural. Regrettably, the first two sets of heads were never thoroughly documented, and their whereabouts remained a mystery. That was until a dedicated team from the School of Geography and the Environment embarked on a ‘Head hunt’.

Dr Katrin Wilhelm and her team delved into the history of these three generations of stone heads. They discovered that each generation was exposed during three distinct periods of atmospheric pollution: the early Industrial Revolution, the Victorian era, and the modern 20th century.

The surface stratigraphies (crust layers) of the sculptures' fabric silently archive this history, serving as a hidden intangible institutional memory or knowledge from the past. This phenomenon, which Dr Wilhelm refers to as “timing pollution”, is part of her research strand titled "Learning from the Past". Here, built structures become ‘material witnesses’ and agents collecting direct and circumstantial evidence of complex environmental interactions.

Photos, left to right: 3rd generation Head at the Sheldonian Theatre (©Wilhelm 2012); 2nd generation Head at Nuneham Courtenay, now in Wytham, which is on display at the Weston Library until July 2019 (©Wilhelm 2017); and 1st generation Head in Worcester College, which is on display at the Weston Library until July 2019 (©Fusade 2017).

When the first two generations of sculptures were relocated to less polluted areas, such as Oxford private and college gardens, their 'pollution clocks' effectively stopped. This presents a unique chance to establish empirical links between stone crust pollution signals (the silent memory) and changing sources of air pollution associated with transport and the industrial evolution.

The originals heads were carved from local weathering resistant Taynton limestone and lasted nearly 200 years. However, they were replaced in 1869 by Victorian replicas. Unfortunately, the second generation was crafted from the softer and more reactive Milton limestone due to some potentially economically-driven decisions.

Like many of Oxford’s buildings at the time, the heads were tarnished by soot and disfigured by acid rain. This was worsened by countless coal fires lit in hundreds of students’ college rooms. Oxford’s air was thick with smoke and its buildings were deteriorating heavily. Only 57 years after post-installation, John Betjeman described the second-generation heads as “mouldering busts”, “unknown bearded guards” and compared them to “illustrations of skin diseases in a medical textbook”. This period coincided with the Historic Buildings Fund (1957–1974), a substantial effort aimed at cleaning-up, repairing, and replacing the Oxford’s historic stone fabric on a large scale.

Due to a shift in conservation ethics and practices, attempts were made to preserve three of the heads using what was then considered cutting-edge technology. Unfortunately, these efforts proved fruitless as the sculptures were beyond saving. Consequently, the University commissioned local sculptor Michael Black to create the current set that now adorns the theatre.

Dr Katrin Wilhelm said:

“Our research has uncovered fascinating insights into urban air pollution history. We studied the layers of black crust that accumulate on stone structures over time, serving pollution level records. By analysing the crusts’ composition, we traced lead pollution sources spanning centuries.”

She further emphasized the broader implications of their findings, "Our insights into the effects of air pollution can aid in long-term environmental impact assessment, inform mitigation strategies and offer a benchmark for evaluating the effectiveness of environmental policies. This, in turn, might inform future urban planning, pollution control, and risk management strategies."

Overall, their research offers invaluable perspectives on air quality history and its impact on stone structures, bolstering essential conservation endeavours and enhancing our grasp on air pollution's long-term consequences.