Testing the Emperors

15th November 2018


Why did the second set of Sheldonian emperor heads weather so much more quickly than the first?

  • Wadham Image - p1000526_1

    Today's Sheldonian Emperor Heads

  • A first generation head in the Wadham gardens

    A first generation head in the Wadham gardens

This was the challenge put to Wadham’s Keeley-Rutherford Junior Research Fellow in Physics, Andrew Princep.

The imposing emperor heads which guard the entrance to the Sheldonian Theatre are in fact the third set of heads, the first set commissioned by Wadham alumnus Sir Christopher Wren and carved by William Byrd in the 1660s.

Researcher Scott Allan Orr, from the School of Geography and the Environment, spearheaded a mission to track down as many of the first and second-generation emperor heads as possible.

The first set, erected on stone plinths in 1669 endured for 200 years and an example of the heads can be found in Wadham’s Fellows’ garden. Their replacements, erected in the 1860s, lasted for half the time and were described by John Betjeman as “the mouldering busts round the Sheldonian”. In 1972, they were replaced by the existing carvings, sculpted by Michael Black.

“We are trying to establish whether they were carved from an inferior stone, or whether the fact that they were installed at the height of the Industrial Revloution made a difference. It is strange that the first generation heads have weathered so much better,”  said Scott, whose research explores built heritage as complex chemical systems in order to understand physical change in response to environmental change.

The application of neutron techinques to material science problems is a new approach explained Wadham’s Andrew Princep, who conducts his research at the ISIS Neutron and Muon Source. 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 damage. Core samples were extracted from three of the second-generation Sheldonian heads, and have been undergoing a variety of tests designed to solve the weathering mystery.

  • A core sample is taken from a second generation head. Photo by Scott Allan Orr

    A core sample is taken from a second generation head. Photo by Scott Allan Orr

  • Wadham Image - sample-camera_distance_0

    The sample was prepared for testing. Photo by Triestino Minniti, STFC/ISIS

The samples 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 chemical make-up.

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 also measures any changes in mineral content that have 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.

“We are hoping that this research will contribute to a large body of literature on the preservation of sandstone,” he added.

  • Andrew Princep

    Andrew Princep

Related news