See Langlois, "Peinture sur Verre." Rouen, 1832; Descamps, "La Vie des Peintres Flamands;" and Gessert, "Geschichte der Glasmalerei." Stutgard, 1839. The antiquity of the glass manufactory of Murano (Venice) is also not to be forgotten. Vasari objects to the Venetian glass, because it was darker in colour than that of Flanders, France, and England; but this very quality was more likely to have an advantageous influence on the style of the early oil-painters. The use of stained glass was, however, at no period very general in Italy.

Zanetti, "Della Pittura Veneziana," marks the progress of the early Venetian painters by the gradual use of the warm outline. There are some mosaics in St. Mark's which have the effect of flesh-colour, but on examination, the only red colour used is found to be in the outlines and markings. Many of the drawings of the old masters, heightened with red in the shadows, have the same effect. In these drawings the artists judiciously avoided colouring the lips and cheeks much, for this would only have betrayed the want of general colour, as is observable when statues are so treated.