What type of glass did Émile Gallé often use for his Art Nouveau vases?

The type of glass Émile Gallé often used for his Art Nouveau vases was cameo glass.

Cameo glass is made by fusing layers of differently coloured glass and then carving or etching through the outer layers to reveal a contrasting design beneath. Gallé used the technique especially effectively for botanical subjects, creating raised or recessed flowers, leaves and landscapes with richly layered colour.

Gallé was born in Nancy in 1846 and became one of the leading figures of the École de Nancy, the French centre of Art Nouveau design. His interest in natural science and botany strongly shaped his glasswork. He also experimented with cased glass, enamel, glass marquetry, metallic effects and deliberate inclusions such as bubbles and textured “patina.”

Cameo glass is sometimes confused with pâte de verre, another French glass technique. Pâte de verre generally involves casting finely ground glass in a mould, whereas Gallé’s cameo decoration typically began with layered glass that was cut or acid-etched. Murano glass refers primarily to a Venetian glassmaking tradition, and Favrile glass is associated with Louis Comfort Tiffany.