Brigitte Simon and Charles Marq are heirs to a long glassmaking tradition in Reims dating back to the 17th century. They created the stained-glass windows of Metz Cathedral from sketches by Marc Chagall. He used an old medieval technique known as plated or doubled glass, consisting of superimposing layers of glass and altering them with acid. It explains why the samples exhibited at the Centre Pompidou-Metz contain so many annotations. They are indicative of extensive research for the right tone of color.