Fortunately, the series of these "Secreta" both commences from a remote date, and is tolerably complete from that to a quite recent period. Scattered allusions to the processes of art and industry may be met with in the writings of several authors of the Alexandrian Neo-Platonic school in the early ages of the Church, from whom the Byzantine Greeks, no doubt, learnt much; but the most ancient collection on the subject is the treatise of Heraclius, or Eraclius, "de Artibus Romanorum."[103] It would appear not to have been written earlier than the 7th or later than the 10th century,[104] its art being, as Mr. Robert Hendrie, the learned translator and editor of the essay of Theophilus, of whom mention will presently be made, observes, "of the school of Pliny, increased, it is true, by Byzantine invention, but yet essentially Roman."[105] The next collection, in point of age, is that published by Muratori,[106] and well known as the "Lucca Manuscript," ascribed by Mabillon to the age of Charlemagne, and by Muratori himself to a period certainly not later than the 10th century. Its Latinity is barbarous, but I scarcely think I can do wrong in following the translation of so careful a writer as Sharon Turner in the following extracts, which treat of illumination, and give us a clear insight into the practice of the school founded under the patronage of the great Frankish emperor of the West. The first I select refers to the preparation of the calf-skin. "Put it under lime and let it lie for three days; then stretch it, scrape it well on both sides, and dry it; then stain it with the colours you wish." The second directs how skins may be gilt. "Take the red skin and carefully pumice and temper it in tepid water, and pour the water on it till it runs off limpid; stretch it afterwards, and smooth it diligently with clean wood. When it is dry, take the whites of eggs and smear it therewith thoroughly; when it is dry, sponge it with water, press it, dry it again, and polish it; then rub it with a clean skin, and polish it again and gild it." Such gilding was effected with gold _leaf_, beaten out between small sheets of "Greek parchment, which is made from linen cloth" (_i.e._ paper), enclosed in vellum. White of egg was used as the mordant for fixing on the gold. The following two passages instruct the student in preparing gold for writing:-- "File gold very finely, put it in a mortar, and add the sharpest vinegar; rub it till it becomes black, and then pour it out. Put to it some salt or nitre, and so it will dissolve. So you may write with it; and thus all the metals may be dissolved. "Take thin plates of gold and silver, rub them in a mortar with Greek salt or nitre till it disappears. Pour on water and repeat it; then add salt, and so wash it. When the gold remains even, add a moderate portion of the flowers of copper and bullock's gall; rub them together, and write and burnish the letters."