"Titian's preferred painting ground was of a red color, and in instances where he did not employ a light , his paintings suffered considerable darkening. Titian never painted directly on the white ground and his paintings... apparently do not carry a multi-colored but rather a neutral underpainting. Glazings on Titian's paintings are not abundant. Only in instances when a color, such as madder lake or , did not lend itself to another application were glazes used. However... glazes might have been removed from some... paintings... during the many cleanings... [I]t is probable that the use of nut oil, which was favored by Italian painters of his time, was responsible for the embrittlement of the paint film. might also have contributed to the darkening... I disagree with those who assert that Titian and El Greco painted on a underpainting."