The conservation of one of the windows in the Upper Library in Mob Quad is featured in this month's issue of Vidimus, the online magazine devoted to medieval stained glass.
Last term, experts from The York Glaziers Trust carefully removed one of the Upper Library's 39 leaded stained glass windows from its lancet in the eastern wall. The window was taken to York, where the Trust carried out cleaning and repair work on the glass.
The Trust have now reinstalled the window, together with specially-constructed protective glazing. This will guard the glass from the elements, preventing compositional decay, further paint loss and deterioration caused by environmental factors, as well as providing a physical barrier against missile damage.
The glass used for the protective glazing, which has been framed to mimic the external bars of the window, is manufactured by the German firm of Lamberts and uses titanium oxide - the same substance contained in sunscreen - to provide UV protection. The sheets of glass are mouth-blown, a process that was used in the production of all window glass until the early 20th century; Lamberts is one of only a few manufacturers still employing this technique to create sheets of glass.
The York Glaziers Trust will monitor the effectiveness of the new protection, and the data they are gathering will help determine the future course of conservation work on the Old Library's precious medieval glass.