The York Glaziers Trust has assembled a team of specialists who are meeting monthly to decide how to tackle the multi-million-pound project and what techniques should be used on a window 78ft tall and 31ft wide.
Like all the stained glass at the Minster, the Great East Window – completed in 1408 – was removed for safety during the First and Second World Wars. Since being reinstalled in 1953, it underwent minor work in the 1970s.
Now, as part of a £30m project at the East End of the Minster, the 301 panels created by John Thornton, of Coventry, are to be removed in phases, cleaned, restored and returned.
The panels include the Son of Man at the centre of the window, which portrays Jesus seated on an altar with a sword in his mouth and his hands outstretched. Kneeling in front is St John the Baptist.
The team of specialists, who will decide what work should be carried out and how it should be done, include the Surveyor of the Minster Fabric, Richard Carr-Archer; and York Glaziers Trust head of conservation Peter Goldsborough.
They have been joined by the professor of medieval studies at York University, Richard Marks; the university's art historian Christopher Norton; English Heritage's specialist on stained glass Sarah Brown and the Minster's development officer Richard Shepherd.
Senior conservator Nick Teed said: "It is such a large scale proposition that it needs to be carefully thought through before we do anything at all. We have removed 12 panels for preliminary assessment from different areas, including the upper tracery."
Some of the panels have buckled badly over the years, while others are extremely dirty. Many have details with glass from other windows which does not match the original and extra lead has been added which today would not be necessary.
Mr Teed said: "As yet the decision still has to be made as to exactly what we do. We need to seek advice from as many specialists as we can, so we are not working in isolation. It leads to a better result."