CONTEXT 177 : SEPTEMBER 2023 19 WORKING WITH GLASS lay in the fabric. This was developed in partnership with project stakeholders, including experts in the field of stained glass and medieval gothic structures, alongside the statutory authorities and consultees. While not always in agreement, all parties contributed to ensuring that the team’s developing proposals were well-reasoned, thoroughly tested and buildable. While the window was stabilised and cordoned off to visitors and the cathedral community below, a four-year research and development phase saw exhaustive investigations to ascertain why the failure had occurred. The team concluded that multiple factors had impacted its structural stability. These included failing medieval drains and unstable ground water levels, corroding ironwork and the impact of previous campaigns of building work. Just as important, the team was able to rule out the possible influences of second world war ordnance damage and the resonance of the fabric from regular bell ringing. Understanding how the window’s history contributed to present day characteristics was essential to developing the conservation strategy. It was discovered that the window had settled over time, bowing and leaning in two directions, and that major repairs had been needed every century to keep the window upright. The compound effects of previous repairs, including the use of ill-matched stone types, meant that its structural elements were not working together. Originally built of Caen stone, the window also had elements of Portland, Doulting, Clipsham and Bath stone that were previously used for repairs. The window was essentially a structure of two facing halves, amazingly glued together with lime, cements and adhesives. While the majority of original stone survived in the tracery, only two original full-depth stones survived in the mullions and transoms. The structural issues were somewhat inherent to the historic 15th-century stone frame, but due to its relative condition and the dearth of original fabric, it was judged that the greater value now lay within the 18th-century-devised assemblage of 12th-century glass. It became clear that the only means of securing this valuable structure as the home of the cathedral’s most precious glass was to fully dismantle it, salvaging and repairing as much stone as possible, supplemented with new Caen stone as required to reconstruct the window. Sustainability is at the heart of Canterbury’s spirit of conservation: the implicit understanding that decisions made will have a long-lasting impact on the longevity of repair. Much can be learnt from the actions of our predecessors as they grappled with their own financial, climatic and ideological context. Beyond conservation decisions on the fabric as an artefact then, prevailing awareness of 1,400 years of continuous change and adaptation to the cathedral fabric, inspired the team to confidently tackle the structural and environmental issues that threatened to undermine the window’s future. Preceding work on the window itself, repairs to the monastic drain and to the vaults of the transept had to be put in hand. With support scaffold restricting access, the cleaning, setting out, measuring, protecting, dismantling, repairs and reinstallation all had to be undertaken by hand. Many of the stones weighed more than 250 kg, some were half a tonne. The re-build tolerance had to be millimetre perfect, with all historic deformities reconstructed exactly, to allow the historic glass to be re-fitted unaltered. Bespoke tools for setting out were developed and manufactured, the success of which is evidenced by not a single glass panel having needed to be adjusted on reinstallation. Two beds of natural stone were employed for renewals. The mined Ferme bed Caen limestone used for piecing repairs to the tracery and jambs was tested to match the characteristics of surviving medieval fabric. The available bed depths could not exceed around 300 mm, so an alternative stone was required for the mullions and transoms of the lower windows. For this, Chauvigny A’grain, a limestone sourced from an opencast quarry near Poitier, has been employed. Modifications to traditional glazing techniques mean that the window retains an authentic appearance.
RkJQdWJsaXNoZXIy MjgyMjA=