The restoration and conversion of the nave of the church into a concert hall provided the opportunity for a thorough study and cleaning of this outstanding group of stained glass windows – part of the Museum’s collection – that decorate the building. Of the 146 stained glass windows – from the plainest ones in geometrical shapes to the great figurative compositions – eighty-one were restored, including twenty Tiffany windows commissioned at the turn of the twentieth century for the American Presbyterian Church on Dorchester Street (now demolished). They were reinstalled in the Erskine and American Church on Sherbrooke Street between 1937 and 1938. It is without a doubt the most important collection of its kind in the country. To allow music lovers who attend concerts and Museum visitors who stroll through Bourgie Hall to appreciate these windows fully, the Museum installed an innovative system of permanent backlighting, the first to be carried out on such a scale.

Eighteen of the twenty Tiffany windows were created during the heyday of the famous Tiffany Glass and Decorating Company in New York, between 1897 and 1904. The ensemble was one of only two commissions by Tiffany in Canada and one of the few surviving religious series in North America. Four of these outstanding double lancet windows are enormous: nearly four metres high and 1.5 metres wide. Some five thousand hours of work and half a million dollars were devoted to restoring the Tiffany windows, the most ambitious project of its kind ever undertaken by the Museum.