gold leaf - An extremely thin foil made of gold. It is available in various colors, each with a different proportion of copper or other metal in the alloy. Leaf made of less expensive material to resemble gold is sometimes referred to as gold leaf. Something to which gold leaf has been applied may be described as gilt or gilded.
Examples of works including gold leaf:
Bernardo Daddi (Italian, Florentine, about 1280-1348), Triptych: Madonna, Saint Thomas Aquinas, and Saint Paul, about 1330, tempera and gold leaf on wood panel, 47 1/2 x 22 inches (120.7 x 55.9 cm), J. Paul Getty Museum, Malibu, CA. See Gothic, Middle Ages, and triptych.
Simone Martini (Italian, Sienese, active by 1315, died 1344), Saint Andrew, possibly c. 1330, tempera on wood panel, gold ground, 22 1/2 x 14 7/8 inches (57.2 x 37.8 cm), Metropolitan Museum of Art, NY. (On the Met's page, you can enlarge any detail.)
Lynda Benglis (American, contemporary), Knossos, 1978, 24 carat gold leaf on plaster, 61 x 20 x 8 inches, Gihon Foundation.
Also see bole, gilding and ormolu.