of Revelation, and the glazier Thornton may have been influenced by earlier illuminated manuscripts on the subject such as the Latin Douce Apocalypse (Oxford, Bodleian Library, Douce MS 180) and the Old French Queen Mary Apocalypse (London, British Library Royal MS BXV). The work was conceived by Archbishop John of Thoresby in the mid fourteenth century, but the window itself was only completed thanks to the funding of Bishop Walter Skirlaw and Archbishop Richard Scrope. Another important window is the tall Five Sisters window. Because of the extended time periods during which the glass was installed, different types of glazing and painting techniques are visible in the different windows. Approximately two million individual pieces of glass make up the cathedral's stained-glass windows. The windows were removed in 1916 because of the fear of bombing during the First World War and the "Five Sisters" window was restored in 1925 with £3,500 raised by Almyra Gray and Helen Little. The glass was removed again during the Second World War. In 2008 a conservation project of the Great East Window commenced, involving the removal, repainting and re-leading of each individual panel. While the window was in storage in the minster's stonemasons' yard, a fire broke out in some adjoining offices, due to an electrical fault, on 30 December 2009. The window's 311 panes, stored in a neighbouring room, were undamaged and were successfully moved to safety. In September 2015, the first phase of the renovation project of the East Front of the Minster was completed. The final phase of the £11 million restoration of the 311 panels was completed in September 2017 and they were re-installed between November 2017 and January 2018. In total, the work on the Great East Window had taken 92,400 hours of labour, including the time required to add protective UV coating on the glass. The work was largely undertaken or overseen by Peter Gibson, who worked on all the Minster's windows during his career. Towers and bells The two west towers of the minster hold bells, clock chimes and a concert carillon. The north-west tower contains Great Peter (216 cwt or 10.8 tons) and the six clock bells (the largest weighing just over 60 cwt or 3 tons). The south-west tower holds 14 bells (tenor 59 cwt or 3 tons) hung and rung for change ringing and 22 carillon bells (tenor 23 cwt or 1.2 tons) which are