in stained glass, technique employing fused layers of coloured glass fragments illuminated from behind, creating an illusion of three-dimensionality in the design. Gemmail is frequently used to reproduce works from other pictorial media. The technique was developed in the late 1930s by the French artist Jean Crotti.

A gemmail is constructed, piece by piece, on a pane of clear glass bearing the outline of the design. When all fragments have been glued in place, the work is dipped in transparent enamel and baked until fused. Works by Picasso, Braque, and Rouault have been reproduced in this medium, and the Franklin D. Roosevelt station of the Paris metro is decorated with a series of gemmaux.