11 January 2012: Britain's oldest and largest specialist stained glass conservation studio has recently embarked upon the conservation of York Minster's Great East Window with help from Carl Zeiss microscopes. The York Glaziers Trust chose a pair of Stemi DV4 Spot microscopes to investigate surface corrosion on Britain's largest expanse of medieval stained glass and the Zeiss AxioCam to record the phenomena for future reference.

According to Sarah Brown, Director of York Glaziers Trust and Course Director of the University of York's MA in Stained Glass Conservation, "The pre-conservation examination and documentation of every panel requires a microscope with a long reach and two newly acquired Stemi DV4 Spot microscopes are now an essential part of the conservators' toolkit in our workshop. The exceptional optics and the superb build quality of these microscopes are ideal for the task. The Stemi DV4 Spot is a delight to use, allowing precision adjustments to be made over the large but fragile panels with the minimum of effort."

Following preliminary photography and documentation, each panel is dismantled to allow the surfaces of the individual glass pieces to be cleaned and restored. Monitoring by microscope is essential to ensure that neither the delicate protective gel layer of the base glass nor the potentially vulnerable paint layers are damaged by the cleaning process. Complete dismantling also allows edge-bonding of original glass pieces to restore damaged pieces prior to re-glazing.

"The Stemi DV4 has also proved invaluable in the investigation of corroded glass surfaces and we are only just beginning to appreciate their full potential," says Sarah. "The laminate glasses, especially the 'flashed' reds used in the window, are especially vulnerable to corrosion and the microscopes are enabling the Trust to record both distinctive and characteristic corrosion phenomena for future reference. The few examples of deliberately abraded ruby glass discovered so far have been of particular interest."

The Minster's Great East Window was commissioned in 1405 from the Coventry glazier, John Thornton, and upon completion in 1408, depicted the beginning and the end of all things. Under a figure of God holding a book with the words 'Ego sum alpha et omega' (I am the beginning and the end), the main lights tell the story of Creation and the events of the Apocalypse. With funding from the Heritage Lottery Fund, the complete restoration of the window and its return with state-of-the-art environmental protection will be completed in 2016. The project will ensure its preservation in close to museum conditions for many generations to come and was the subject of BBC4's recent documentary, 'Britain's Most Fragile Treasure'.

With a 4:1 zoom range and a 92mm working distance, the Stemi DV4's best-in-class, parfocal zoom optics enable distortion-free imaging over the whole of the large object field. Digital and video cameras may be rapidly connected for image capture and recording and the system is also fully-compatible with Zeiss AxioVision imaging and archival software. Other options available for the Zeiss Stemi DV4 Stereomicroscope include transmitted-light darkfield equipment, eyepiece measuring devices, and attachment systems that enable enhanced resolution magnification up to 64x.