 In addition, specialist cleaning techniques are used to remove accumulated chemical deposits which are very damaging to the building.As regards the interior, priorities include decoration of the vaults of the Trinity Chapel, major improvements to the Treasury building which contains, amongst other things, the choir practice rooms, and conservation work in several other chapels.The earliest coloured glass windows in the cathedral date from the late 12th century, whilst others are as new as the four Ervin Bossányi windows in the south-east transept (1957).