In the 19th century, large parts of the cathedral’s original stonework was replaced with the aim of preserving the intricate windows and carvings.
However, the stone chosen has since reacted badly to the elements and now key parts of the building are suffering from significant erosion.
Alex McCallion, the director of works and precinct at the Minster said: “They used the best knowledge available and the work was done with good intentions, but unfortunately it hasn’t stood the test of time.
“What’s great about this project, and many others within the cathedral, is that we are now using stone from the original seam in Tadcaster from which the Minster was built.”
Work to erect scaffolding around the window has begun, but will not be completed until May and the painstaking restoration will take a number of years.
Mr McCallion added: “All the glass has to be removed before we can start on the stone, but our expert masons have already completed a lot of the decorative work. This is an enormous project, but absolutely worth it to see this important window restored to its original glory.”