Silver staining is the glass-painting technique that uses fired silver compounds to produce yellow on stained glass.
The technique was developed in the early 14th century and transformed the possibilities of medieval glass painting. A silver compound, commonly based on silver nitrate or silver sulfide, is applied to the surface of the glass. When the piece is fired in a kiln, silver ions penetrate the glass and create yellow, amber, or orange tones.
Silver stain allowed artists to add details and color without joining another piece of glass with lead. It was especially useful for painting hair, crowns, architectural highlights, foliage, and other small areas. The final shade depends on the compound, firing conditions, and the glass composition.
Silver staining is not the same as enameling. Enamel is a powdered glass paint that forms a colored layer on the surface, while silver stain chemically alters a shallow zone of the glass itself during firing.