Grisaille is the stained-glass technique that uses gray or black paint to add details to glass.
The word comes from the French term for a gray monochrome treatment. In glassmaking, grisaille paint is usually made from finely ground glass particles mixed with a metallic oxide or other coloring material. The artist applies it to the surface, then fires the piece so the paint fuses permanently with the glass.
Grisaille can create facial features, folds in clothing, lettering, architectural lines, shadows, and broad areas of modeling. Medieval glaziers used it extensively because it allowed a workshop to turn colored or clear glass into detailed narrative imagery without cutting every visual detail into separate pieces.
Grisaille is not the same as silver stain. Silver stain produces yellow or amber tones after firing, while grisaille normally supplies dark linear or shaded detail. Enamel is a broader category of fired glass paint and can include colored paints beyond gray and black.