Before moving on, a quick word about the paints. The Italians, you will recall, primarily specialized in frescos, and it was the Northerners who developed oil artwork. Tempera was a paint made of dry pigments, or colors, which were mixed with a binding material. Fra Angelico's Annunciation was painted with tempera onto a wood canvas. Gesso was a mixture of glue and a white pigment such as plaster, chalk, or white clay. Oil paints, on the other hand, consisted of a mixture of dry pigments with oils, turpentine, and sometimes varnish. The artists took these mixtures and made transparent, smooth glazes or thick, richly textured surfaces. Oil paints were used as glazes over the originals, but eventually the artists just used the oil mixture alone to paint. An added benefit of oil paints was that their drying time was much longer than that of other paints, allowing artists more time to work. The oil also added a brilliant glazy appearance to the finished work.