Colours of all kinds prepared from vegetable or animal substances required a special treatment to fit them for use as pigments in solid or _tempera_ painting. Though indigo and other colours of a similar class are the best and simplest of dyes for woven stuffs, yet they are too thin in body to use alone as pigments. Thus both in classical and mediaeval times these dye-pigments were prepared by making a small quantity of white earth, powdered chalk or the like absorb a large quantity of the thin dye, which thus was brought into a concentrated and solid, opaque form, not a mere stain as it would otherwise have been. These kinds of pigments are described by Pliny, _Hist. Nat._ XXXV. 44 and 46; and by Vitruvius, VII. xiv. Eraclius in his work on technique, _De artibus Romanorum_, calls them _colores infectivi_, "dyed colours," an accurately expressive phrase. One method, occasionally used for the cheaper class of manuscripts, was to paint on to the vellum with white lead, and then to colour it by repeated application of a brush dipped in the thin dye-pigment. Many of the colours mentioned below belong to this class. _Terra verde._ _Green pigments._ A fine soft green much used in early manuscripts is a natural earthy pigment called _terra verde_ or green _Verona earth_. This needs little preparation, except washing, and is of the most durable kind; it is a kind of ochre, coloured, not with iron, but by the natural presence of copper. _Verdigris green._ A much more brilliant green pigment was made of _verdigris_ (_verderame_) or carbonate of copper, produced very easily by moistening metallic copper with vinegar or by exposing it to the fumes of acetic acid in a closed earthen vessel; see Theophilus, I. 37. _Verdigris green_ was much used by manuscript illuminators, especially during the fifteenth century, when a very unpleasant harsh and gaudy green appears to have been popular. When softened by an admixture of white pigment, verdigris gives a pleasanter and softer colour. _Chrysocolla._ A native carbonate of copper, which was called by the Romans _chrysocolla_[272], was also used for mediaeval manuscripts. It is, however, harsh in tint if not tempered with white. Both the last-named pigments were specially used with yoke of egg as a medium. _Prasinum_, a vegetable green made by staining powdered chalk with the green of the leek, was sometimes used. Cennino Cennini also recommends a grass green made by mixing orpiment (sulphuret of arsenic) and indigo. One of the best and most commonly used greens was made by a mixture of smalto blue and yellow ochre; other mixtures were also used. _Red pigments._ Red and blue are by far the most important of the colours used in illuminated manuscripts, and it is wonderful to see what variety of effect is often produced by the use of these two colours only. _Vermilion and minium._