_Cheap methods._ Inferior processes were sometimes used for the cheap manuscripts of later times. Thus tin leaf burnished and then covered with a transparent yellow lacquer or varnish made from saffron was used instead of gold. Cennino and other writers describe a curious method of applying gold easily and cheaply. The illuminator was first to paint his design with a mixture of size and pounded glass or crystal; this, when dry, left a surface like modern sandpaper or glass-paper, the artist was then to rub a bit of pure gold over the rough surface, which ground off and held a sufficient amount of gold to produce the effect of gilding. Only a very coarse effect, worthy of the nineteenth century, could have been produced by this process. CHAPTER XV. THE MATERIALS AND TECHNICAL PROCESSES OF THE ILLUMINATOR (_continued_). _Vehicles used._ _The coloured pigments of the illuminators._ Though mediaeval manuscripts are splendid and varied in colour to the highest possible degree, yet all this wealth of decorative effect was produced by a very few pigments, and with the simplest of _media_, such as _size_ made by boiling down shreds of vellum or fish-bones[264], or else gum-arabic, or occasionally white of egg or a mixture both of the yoke and the white[265]. In the main the technique of manuscript illumination is the same as that of panel pictures executed in distemper (_tempera_). An oil medium was unsuited to manuscript work because the oil spoilt the beautiful opaque whiteness of the vellum and made the painting show through to the other side[266]. _Ultramarine blue._ _Blue pigments._ The most important blue pigment, both during classical and mediaeval times, was the costly and very beautiful _ultramarine_ (_azzurrum[267] transmarinum_), which was made from _lapis lazuli_, a mineral chiefly imported from Persia. This _ultramarine_ blue was the _cyanus_ or _coeruleum_ of Theophrastus and Pliny. It is not only the most magnificent of all blue pigments, but is also the most durable, even when exposed to light for a very long period. _Its manufacture._ The general principle of the manufacture of ultramarine is very simple; consisting merely in grinding the _lapis lazuli_ to powder, and then separating, by repeated washing, the deep blue particles from the rest of the stone[268]. The process of extracting the blue was made easier if the _lapis lazuli_ was first calcined by heat. This is the modern method, and was occasionally done in mediaeval times, but it injures the depth and brilliance of the pigment, and in the finest manuscripts ultramarine was used which had been prepared by the better though more laborious process without the aid of heat. _Its great value._ The proportion of pure blue in a lump of _lapis lazuli_ is much smaller than it looks; the stone was and is rare and costly, and thus the finest ultramarine of the mediaeval painters was often worth considerably more than double its weight in gold[269].