The chapter house vestibule, York Minster, c1300
These three windows (CH nIX, sV and sVII) are among the oldest in the Minster and having had no external protection during their seven-hundred year history, the glass is now heavily corroded and in places is paper-thin, especially in window nIX.
Despite the irreversible darkening of some of the white glass, much of the pot-metal coloured glass, especially in windows sV and sVII, had retained its brilliance under layers of surface dirt and extremely heavy mending leads.
Cleaning under the microscope has revealed for the first time since the 1920s the exceptional quality of both glass and glass-painting. The careful removal of some of the mending leads has allowed the original design to re-emerge from obscurity. Following conservation in 2008-9, the windows are now safeguarded with external protective glazing, which will halt the processes of glass deterioration that threatened their future.