To make ink, cut for yourself wood of the thorn-trees in April or May, before they produce flowers or leaves, and collecting them in small bundles, allow them to lie in the shade for two, three, or four weeks, until they are somewhat dry. Then have wooden mallets, with which you beat these thorns upon another piece of hardwood, until you peel off the bark everywhere, put which immediately into a barrelful of water. When you have filled two, or three, or four, or five barrels with bark and water, allow them so to stand for eight days, until the waters imbibe all the sap of the bark. Afterwards put this water into a very clean pan, or into a cauldron, and fire being placed under it, boil it; from time to time, also, throw into the pan some of this bark, so that whatever sap may remain in it may be boiled out. When you have cooked it a little, throw it out, and again put in more; which done, boil down the remaining water unto a third part, and then pouring it out of this pan, put it into one smaller, and cook it until it grows black and begins to thicken, add one third part of pure wine, and putting it into two or three new pots, cook it until you see a sort of skin show itself on the surface; then taking these pots from the fire, place them in the sun until the black ink purifies itself from the red dregs. Afterwards take small bags of parchment carefully sewn, and bladders, and pouring in the pure ink, suspend them in the sun until all is quite dry; and when dry, take from it as much as you wish, and temper it with wine over the fire, and, adding a little vitriol, write. But, if it should happen through negligence that your ink be not black enough, take a fragment of the thickness of a finger, and putting it into the fire, allow it to glow, and throw it directly into the ink. The next collection of "Secreta," in point of importance and probably antiquity, is the "Mappæ Clavicula," or "little key to drawing," a manuscript treatise on the preparation of pigments, and on various processes of the decorative arts practised during the Middle Ages, in the possession of Sir Thomas Phillipps, of Middle Hill.[109] The proprietor of the volume, Mr. Hendrie, Sir Charles Eastlake, and (last, not least) Mr. Albert Way, agree in considering it highly probable that it may be an English collection, probably of about the reign of Henry II. Like the "Schedula" of Theophilus, it presents a very miscellaneous series of recipes, and tends to prove, what is very generally believed by the learned, that the "Masters of Arts" of old were frequently skilled, not in special departments of production, such as the modern division-of-labour system has created, but in multifarious avocations, such as we should not now readily recognize as likely to be practised by any single individual.