A team of researchers from the University of Oxford are hoping that the STFC’s ISIS facility will help them solve a local mystery – why a set of busts that stood outside of the Sheldonian Theatre in Oxford crumbled beyond recognition within a few short decades when their predecessors endured for two centuries. Did the mason simply use inferior quality stone, or was some 19th century student skulduggery to blame?
A sample of the head is undergoing tests at the STFC's ISIS Neutron and Muon Source.
(Credit: Scott Orr)
In the later half of the 17th century, a young Christopher Wren (he of Saint Paul’s Cathedral fame) embarked on what was only his second commission – the design and construction of the Sheldonian Theatre for the University of Oxford. Upon its completion in 1668, Wren commissioned the carving of 14 stone heads that would stand to mark the theatre’s boundary.
The heads, carved by William Byrd, a mason and stonecutter who worked nearby, were completed in 1669 and erected on stone plinths. No one knows for certain what the sculptures – a selection of male heads each sporting a magnificent beard – were intended to represent, but they became known as the “Emperors”. The enigmatically hirsute carvings remained outside the Sheldonian Theatre for 200 years until, crumbling and weathered, they were replaced with new sculptures.
Unfortunately, the replacements proved to be far less durable and they succumbed to the elements with startling speed. In fact, by 1925, just 57 years after their erection, their state was so appalling that John Betjeman, described them as “the mouldering busts round the Sheldonian” and, in 1972, their crumbling visages were replaced with a third set of carvings.
So what was it that caused the second reign of the Emperors to be so blighted by decay? One theory is that they were simply made of inferior quality stone, while another claims that the heads were vandalised by undergraduates from Oxford University who daubed the heads with paint and it was the subsequent harsh cleaning they received that caused their rapid decline.
Many of the original Emperors and their ill-fated heirs were lost over the years but, following a national appeal by the University of Oxford’s School of Geography and the Environment, earlier this year, several of the busts were located – many languishing as garden ornaments.
With some of the heavily deteriorated busts now in hand, it was decided that they should be studied to determine how the heads had weathered in order to improve the conservation of the third generation of Emperors.
Core samples were extracted from three of the second generation Sheldonian heads (at half a tonne each, they were too heavy to study directly) and sent down the road to the STFC’s ISIS Neutron and Muon Source in Didcot. Under the guidance of Dr Scott Orr, of the School of Geography and the Environment, Oxford University, and Dr Andrew Princep, of STFC and Wadham College, Oxford University the samples have been undergoing a barrage of tests designed to solve the mystery once and for all.
ISIS uses neutrons to investigate objects in a non-destructive fashion. Neutrons are a powerful probe of materials because they are electrically neutral and can penetrate deep inside a sample without causing damaging. The samples under study are bombarded with millions of neutrons a second, which either pass straight through or are scattered off the atoms and molecules within in it. By studying the scattered neutrons, a map can be built up of the sample’s structure and its chemical make-up determined.
ISIS’s GEM (General Materials Diffractometer) is being used to look at the composition of the stone and how weathering and corrosion has affected it. It will also measure any changes in mineral content that has occurred over time. Another instrument, a neutron imager called IMAT, has already been able to determine there are some ‘components of interest’ in the sample. Whether or not those ‘components’ turn out to be evidence of 150-year-old undergraduate tomfoolery remains to be revealed.
Last updated: 25 February 2019