The Great East Window, currently hidden beneath about 16 miles of scaffolding as it is cleaned and restored, was painted by a Medieval stained glass painter, John Thornton, between 1405 and 1408. One of the leading stained-glass craftsmen of his day, Thornton was paid about £56 for his three-year effort, in 1408. Some estimates suggest that the payment would be worth about £300,000 today. According to an article in the Yorkshire Post, the current cost of cleaning and restoring the Great East Window is about £6 million. The BBC has reported that the job could take as long as 15 years.
Maintaining the Minster's amazing Medieval windows is a full time job. There are 128 stained glass windows, containing about 2 million individual pieces of Medieval glass. To be cleaned, each window must be taken apart so that each piece of stained glass can be individually cleaned. Then the windows are reassembled and re-leaded. Each window is cleaned about once every 125 years. To do all the windows at once would take about 200 years!