In the Italian school of the time of Raphael the grounds were generally composed of pipe-clay mixed with chalk; and such are decidedly the most durable. Claude frequently used a similar composition; and the consequence is, that we find the skies, distances, and delicate passages as clear as the day they were painted. Nothing, indeed, is better established than that white grounds are in every way preferable. Sir Charles Eastlake observes (Goethe on Colours, p.378), "the secret of Van Eyck and his contemporaries is always assumed to consist in the vehicle he employed; but a far more important condition of the splendour of colour of the works of those masters was the careful preservation of internal light by painting thinly, but ultimately with great force, on white grounds." It matters not, however, whether the brightness reside in the ground, or is reproduced at any stage of the work. Thus, Titian frequently obtained the effect of luce di dentro (light within), so much extolled by the Italians, by painting with white opaque colour over the dark or red grounds he frequently employed, and then glazing over this opaque colour.