The circular glass-window that dominates, with its 6 meters diameter, the apse of the Sienese Duomo, is undoubtedly one of the most important works of art built with such technique during medieval Italy. For such works it was obviously necessary a team work with several other specialized artists: a painter to set up the whole project and a craftsman glassmaker who provided shaping and assemblage of all the colored glasses. In the middle, bottom to top, you can see represented the "Burial, Assumption and Coronation of the Virgin", whom the Sienese cathedral is entitled; all around her you can see the Patron Saints of the town and the four Evangelists.


It is a major work in Duccio's artistic path, whose importance has been acknowledged in relatively recent times: its dating has been delayed of almost a hundred years because the wall in which the oculus opens was only built during the second half of the 14th Century. Enzo Carli was the first, in a 1946 crucial essay where he crossed both documentary informations and stylistic analysis, to reclaim Duccio the original project of the work, at first intended for the original thirteenth-century Duomo apse, later moved to its current position only in 1360-65, when it went through the first of the several restorations to come.


Considering the extreme fragility of this technique and the several restorations, the Sienese glass-window came to us in a considerably good state: the replaced glasses are just a few, and in some cases you can still see the black brush sketch defining, directly on the colored glass panes, the smallest and most defined details of the figuration (from the features of the faces to the creases in the clothes). This drawing, the most delicate part of the work, is so perfect one can easily think the hand that traced it was probably Duccio's himself.


In the glass-window Duccio adopts some spatial expedients to enliven the strictly geometric structure of such work.; for instance in those cases where the figuration pops out of the frame borders: see the throne base on which the "Coronation" takes place, the wings of the angels sustaining the almond with Our Lady of the Assumption or the figure of the angel accompanying Saint Matthew.