See especially pages 24 to 28 inclusive, from which I transcribe a few elegant and suggestive passages:—
"The student should keep," says Mr. Jewitt, "both in form and colour, as near to Nature as possible. No fantastic design can be so elegant as one copied and studied from Nature. What, for instance, can be more beautiful or more appropriate for intertwining with rich scroll-work than the convolvulus, the maurandia, the woodbine, the tropeolum, or the passion-flower? These painted upon a rich groundwork of diapered gold, or upon one of the beautiful grounds of the 15th century, composed of gold and blue or green, in fine waved or winding lines, crossing each other in every conceivable direction, form truly elegant studies, for almost all varieties of ornamentation. Whenever birds, insects, &c., are introduced, they should, as a general rule, be drawn true to nature; but they may, nevertheless, be turned and twisted into almost any position or shape. For instance, a lizard, with its beautiful emerald-green back, its yellow underparts, and rich brown mottlings, might be introduced with its long tail wrapped and twisted round the stem of a plant, and its little head, with brilliant eyes, shown just peeping out from under one of the beautiful flowers. The ladybird, with its bright red wings, covered with small black spots, might also be well introduced, creeping upon a leaf or stem. Hairy caterpillars, ants, beetles, snails, glow-worms, and even spiders, form also beautiful additions to a design, and may be introduced in almost any form or shape. Butterflies and moths, in their endless and beautiful variety, with their wings of every conceivable colour and shade, and of the most exquisite forms, are truly amongst the most beautiful and appropriate objects which the student can have for his mind to dwell upon. But not only these,—for occasionally a squirrel might be introduced perched upon the scroll-work; a cat, a goat, a dog, a monkey peeping out from behind a leaf; or, indeed, any animal, if artistically and naturally treated, may be introduced with really good effect. Flowers, fruits, shells, corn, &c., all add their beauties to a design; and, indeed, there is nothing in nature, no, not one object, but which may well be introduced into ornamental designing, and may be so translated and poeticised as to become appropriate to any subject."
"Materials for a History of Oil-painting," by Charles Lock Eastlake: London, 1847.
The most copious text of Heraclius is contained in the Le Bègue collection of writers on art, brought together by Master John Le Bègue, of Paris, in the 15th century.
Sir Charles Eastlake does not place Heraclius so early as Raspe and Mr. Hendrie do. I incline to agree with the last-named critics.
The text of Heraclius is given not from the Le Bègue manuscript, but from one less perfect, formerly at Cambridge, but now in the British Museum, Egerton 840 A, in Raspe's work—"A Critical Essay on Oil-painting." London, 1781.