Oil-based paints are introduced by mixing powdered pigments with linseed or walnut oil. They quickly gain in popularity because they dry very slowly, giving the artist greater control and more freedom to make changes. Oil paints are a great improvement over fresco and tempera, as both techniques required special preparation and materials and allowed the painter little control. By end of the 15th century, oil painting had become an important part the painters' technical repertoire. This detail shows how Giovanni Agostino da Lodi used the new oil paints to give amazing detail to the curls in the angel's hair.