A painting medium composed of pigments that are mixed with egg, glue, or casein. Until the introduction of oils in the 15th century, tempera was the medium used for panel painting, normally applied over a smooth coat of white gesso. The advantage of tempera is that it is fast drying and produces brilliant colors and clear, sharp outlines. The disadvantage is that it is an opaque medium that does not lend itself to transparent effects. Once oils were introduced, many 15th- and 16th-century masters used oil overlays over a tempera underpainting to achieve both the luminosity of oil paints and the precision of tempera.
Historical dictionary of Renaissance art. Lilian H. Zirpolo. 2008.