107. The modes of bleaching and thickening oil in the sun, as well as the siccative power of metallic oxides, were known to the classical writers, and evidence exists of the careful study of Galen, Dioscorides, and others by the painters of the twelfth and thirteenth centuries: the loss (recorded by Vasari) of Antonio Veneziano to the arts, "per che studio in Dioscoride le cose dell'erbe," is a remarkable instance of its less fortunate results. Still, the immixture of solid color with the oil, which had been commonly used as a varnish for tempera paintings and gilt surfaces, was hitherto unsuggested; and no distinct notice seems to occur of the first occasion of this important step, though in the twelfth century, as above stated, the process is described as frequent both in Italy and England. Mr. Eastlake's instances have been selected, for the most part, from four treatises, two of which, though in an imperfect form, have long been known to the public; the third, translated by Mrs. Merrifield, is in course of publication; the fourth, "Tractatus de Coloribus illuminatorum," is of less importance. Respecting the dates of the first two, those of Eraclius and Theophilus, some difference of opinion exists between Mr. Eastlake and their respective editors. The former MS. was published by Raspe,[14] who inclines to the opinion of its having been written soon after the time of St. Isidore of Seville, probably therefore in the eighth century, but insists only on its being prior to the thirteenth. That of Theophilus, published first by M. Charles de l'Escalopier, and lately from a more perfect MS. by Mr. Hendrie, is ascribed by its English editor (who places Eraclius in the tenth) to the early half of the eleventh century. Mr. Hendrie maintains his opinion with much analytical ingenuity, and we are disposed to think that Mr. Eastlake attaches too much importance to the absence of reference to oil-painting in the Mappae Clavicula (a MS. of the twelfth century), in placing Theophilus a century and a half later on that ground alone. The question is one of some importance in an antiquarian point of view, but the general reader will perhaps be satisfied with the conclusion that in MSS. which cannot possibly be later than the close of the twelfth century, references to oil-painting are clear and frequent.