What is the difference between underglaze and overglaze enamel colors? Underglaze decoration is applied to a ceramic body under a transparent glaze before the piece is fired, making it one of the most permanent kinds of ceramic decoration. Underglaze painting requires the use of pigments that can be fired at high temperatures, such as those derived from cobalt, iron, and copper. Overglaze enamels are applied to ceramics after they have been glazed and fired once. The colors are painted on the piece, and then a second firing at a lower temperature is required to fix the colors.