The reason for this method is not apparent. Possibly it was first done as a means of utilizing waste clippings of the costly red cloth, and then, when the habit was established, no other method was known to the colour-makers, who in some cases bought pieces of cloth on purpose to cut them up and use in this way[277]. The _scarletum blanketum_ mentioned at page 234 was bought for this purpose. _Madder._ _Madder-red_ was also used as a pigment by boiling the root of the madder-plant (_rubia-tinctorium_), and then using the concentrated extract to dye powdered chalk. Various red and purple flowers, such as the violet, were used in the same way as _colores infectivi_. _Lac._ _Lake-red_ (_lacca_ or _lac_) was made and called after a natural gum or resin, the _lach_ of India; see Cennino Cennini, § 44. This is a beautiful transparent colour, which, in some fine manuscripts of the fifteenth century, is used as a transparent glaze over burnished gold, the effect of which is very magnificent, as the metallic gleam of the gold shines through the deep transparent red of the over-painting. Lake was also used as an opaque, solid pigment by mixing it with white, which at once gave it "body," and destroyed its transparency. _Purple_ of a very magnificent tint was occasionally made by a mixture of _ultramarine_ with the carmine-red of the kermes beetle; this was specially used by the illuminators of the fourteenth and fifteenth centuries. _Yellows._ _Yellow ochre_, a fine earth pigment coloured by iron, was the principal yellow of the illuminators. In late manuscripts _orpiment_ (sulphuret of arsenic), which is a more brilliant lemon-yellow, was occasionally used; see Cennino Cennini, § 47. _Litharge yellow_, an oxide of lead, was another important colour, but more especially for the painter in oil, who used it very largely as a drier[278]. Another fine ochreous earth of a rich brown colour was the _terra di Siena_ or "raw Siena"; the colour of this was made warmer in tint by roasting, thus producing "burnt Siena." _Use of white._ _White pigments_ were perhaps the most important of all to the illuminator, who usually only used pure colours for his deepest shadows; all lights and half tints, both in miniature pictures and in decorative foliage, being painted with a large admixture of white. The use of this system of colouring by Fra Angelico and many painters of the Sienese school has been already referred to; see page 190. For this reason it was very important to use a pure and durable white pigment which would combine well with other colours. Lime white. _Bianco di San Giovanni_ was in all respects one of the best of the whites used by illuminators.