The coloring agent in paint.
The coloring agent in paint. The paints used in illumination consist of vegetable, mineral, and animal extracts, ground or soaked out and mixed with glair as a binding medium, perhaps with some glue and water added. Other additives were also used, including stale urine, honey, and ear wax, to modify color, texture, and opacity; inert whites such as chalk, eggshell, or white lead were added to increase opacity. Some pigments were obtained locally (such as turnsole, or crozophora tinctona); others were exotic imports (such as ultramarine, made from lapis lazuli imported from Persia or Afghanistan). During the early Middle Ages, scribes and/or illuminators ground and prepared their own pigments, perhaps with the aid of an assistant, but with the growth of specialized, more commercial production around 1200, they often purchased their ingredients in prepared form from a stationer or an apothecary. With the rise of experimental science and international trade in the fourteenth century, many colors were added to the traditional palette, which significantly affected styles of illumination. The production of synthetically manufactured pigments (such as mercury-based vermilion and copper blues) and imports (such as saffron yellow from crocus stamens and red lakes from Brazil woods largely imported from Ceylon) increased at this time. Pigments are difficult to identify precisely without chemical analysis, although other techniques of analysis, such as radiospectroscopy and X-ray fluorescence, as well as reconstructions from medieval recipes, are advancing rapidly. Some pigments also change in a consistent fashion over time: for example, the red lead often used for rubrics frequently fades and turns silver-black through oxidation, and copper-based verdigris green sometimes eats through the support as it corrodes.
Michelle Brown, Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).