[Footnote 302: The idea that the brilliant colouring of the Venetian school was owing to the use of a peculiar vehicle for the colours, or a certain varnish, has been long entertained by artists and connoisseurs; and the opinion has been sanctioned by great names: yet it is highly probable that the great secret of the Venetian painters consisted not in vehicles nor in varnishes, but in employing mineral colours, and in laying them on the canvas as little mixed as possible. No colour derived from the vegetable kingdom will stand well when mixed with oil, and our best colours are composed of metallic oxides, or earthy bodies highly charged with those oxides. When colours are much mixed on the palette they become invariably muddy, and to him who aims at brilliancy of colouring no maxim is of greater consequence than _to keep his palette as clean as possible_. The use of transparent colours in the shadows is another great cause of brilliancy, and this cannot be obtained by the use of mixed colours. It is produced by what is called glazing, or laying transparent colours one over another. In nothing is the effect of glazing, in giving transparency, more obvious, than in the astonishing clearness of the skies and water in the works of the best Dutch artists. That the magical effect of Kuyp's pictures is thus produced, I had an opportunity of knowing, from the blunder of a picture-cleaner, who thought he had made a great discovery when he found the _Rhine_ of a deep blue in a picture by this master; from which, along with the varnish, he had removed a thin coating of yellow, with which the blue was glazed over, to produce the beautiful greenish hue of the water. (_Note by_ Dr. Traile.)] [Footnote 303: Tom. i.] [Footnote 304: His name alone survives in Perugia; though it is believed that one of his pictures remains in the church of S. Angelo Magno, at Ascoli, where the figure of S. Giovanni is ascribed by Lazzeri, in his _Ascoli in Prospettiva_, to one Giandomenico da Perugia, and the landscape to Gio. Francesco da Bologna, that is to say, to Grimaldi. The figure is in the Guercino taste, according to the opinion of Sig. Orsini; but I cannot conceive how he or the Sig. Mariotti (p. 273) should not have remarked that it must be the production of Giandomenico Cerrini, of Perugia, contemporary with Grimaldi and Guercino, and not of that Domenico, the painter of wooden scenes, who lived about an age anterior to them.] [Footnote 305: Lett. Pittoriche, tom. ii. p. 69.]