These collections remarkably illustrate the class of knowledge likely to have been possessed by such apparently versatile geniuses as St. Dunstan, St. Eloi, Bernward of Hildesheim, Tutilo the monk of St. Gall, and many others. The author of the "Mappæ Clavicula," in a few lines of poetical introduction to his teachings, defines the first necessity for painters to be, a knowledge of the manufacture of colours, then a command over the various modes of mixing them, then dexterity in using and heightening them in different kinds of work; and, ultimately, he commends to their attention a variety of information for the advancement of art generally, derived from the writings of many learned men.--"Sicut liber iste docebit." Thus under two hundred and nine heads, but with some tautology, he proceeds to treat, as Sir Thomas Phillipps observes, not only of the composition of colours, but "of a variety of other subjects, in a concise and simple manner, and generally very intelligibly; as for instance, architecture, mensuration of altitudes, the art of war, &c." Among the recipes, in addition to those referring to pigments, are many relating to illuminating. The following, for instance, is curious as defining clearly what were the best and most important tints for illumination:-- _Of different Colours._ "These colours are clear and full-bodied for vellum:--Azorium (azure), Vermiculum (vermilion), Sanguis Draconis (dragon's blood), Carum (yellow ochre), Minium (red lead), Folium (madder purple), Auripigmentum (orpiment), Viride Græcum (acetate of copper), Gravetum Indicum (indigo), Brunum (brown), Crocus (yellow), Minium Rubeum vel Album (red or white lead), Nigrum Optimum ex carbone vitis (the best black made from carbonized vine twigs); all these colours are mixed with white of egg." The mixture of colours appears to have been reduced to a perfect system, each hue having others specially adapted and used, for heightening and lowering the pure tint; thus the author gives directions which are likely to be scarcely less useful to the illuminator of the present day than they were to those of old. _Of Mixtures._ "If, therefore, you should desire to know the natures and mixtures of these [the above given] colours, and which are antagonistic to each other, lend your ear diligently.