"It is therefore clear," says Mr. Eastlake, "that an oil varnish, composed either of inspissated nut oil, or of nut oil combined with a dissolved resin, was employed on gilt surfaces and pictures, with a view to preserve them, at least as early as the fifth century. It may be added that a writer who could then state, as if from his own experience, that such varnishes had the effect of preserving works 'for a long time,' can hardly be understood to speak of a new invention."—P. 22.
Linseed-oil is also mentioned by Aetius, though still for medicinal uses only; but a varnish, composed of linseed-oil mixed with a variety of resins, is described in a manuscript at Lucca, belonging probably to the eighth century:—
"The age of Charlemagne was an era in the arts; and the addition of linseed-oil to the materials of the varnisher and decorator may on the above evidence be assigned to it. From this time, and during many ages, the linseed-oil varnish, though composed of simpler materials (such as sandarac and mastic resin boiled in the oil), alone appears in the recipes hitherto brought to light."—Ib., p. 24.
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 Mappæ 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.
108. Nothing is known of the personality of either Eraclius or Theophilus, but what may be collected from their works; amounting, in the first case, to the facts of the author's "language being barbarous, his credulity exceptionable, and his knowledge superficial," together with his written description as "vir sapientissimus;" while all that is positively known of Theophilus is that he was a monk, and that Theophilus was not his real name. The character, however, of which the assumed name is truly expressive, deserves from us no unrespectful attention; we shall best possess our readers of it by laying before them one or two passages from the preface. We shall make some use of Mr. Hendrie's translation; it is evidently the work of a tasteful man, and in most cases renders the feeling of the original faithfully; but the Latin, monkish though it be, deserved a more accurate following, and many of Mr. Hendrie's deviations bear traces of unsound scholarship. An awkward instance occurs in the first paragraph:—