Note: Do not rely on this information. It is very old.
IlluminationIllumination, the art of adorning MSS. and books with paintings and ornamental letters and designs. The paintings in medieeval MSS. were called miniatures from the frequent use of a red pigment named minium: they were necessarily very smail, a circumstance which gave rise to the modern meaning of the word. Certain Egyptian papyri are extant, in which directions concerning ritual are written in red ink to render them more conspicuous (a method also employed in mediaeval liturgies; hence the term rubric), and even coloured pictures are sometimes introduced. With this exception there are no illuminated MSS. older than the 4th century A.D. The most ancient are the Dioscorides at Vienna, and the Virgil in the Vatican; in both the ornament consists of rectangular pictures. The Codex Argenteus (c. 360), now at Upsala, containlg Ulfilas's translation of the Bible into Meso-Gothic, exhibits a different style of illuminating; here the letters are of gold and silver, and the vellum on which they are written is stained with a red-purple dye - an art the secret of which was afterwards lost. One of the most conspicuous features of the Byzantine style is the abundant use of gold, especially in backgrounds. Byzantine inuence can be more or less clearly discerned in all subsequent styles up to the 11th century. Even the Keltlc style which grew up in the Christian monasteries of Ireland, reaching its zenith in the beautiful Book of Kells (probably a work of the 9th century), is believed to have been of Byzantine origin. The Keltic MSS., however, display a skill in the minutiae of draughtsmanship which is unrivalled in any other syle; their most remarkable characteristic is the extraordinary intricacy of the designs, consisting usually of spirals, ribbon-patterns, and interlaced forms of attenuated animals and birds. The Keltic style was carried by the Irish missionaries to the Continent, where it united with Roman and Byzanne elements in the formation of the Carlovingian style, which grew up in France and Germany under the encouragement of Charlemagne. The Harleian Codex Aureus in the British Museum is a magnificent example of the Carlovingian period. Of the English style, which corresponded to the Carlovingian abroad, the finest example is the benedictional of Ethelwold, Bishop of Winchester (963-84), now at Chatsworth. The art declined owing to the excessive care bestowed on the ornamentation of detail, whilst the writing itself was neglected. In themselves, however, the paintings in MSS. of the 14th and 15th centuries surpass those of any preceding age. The most beautiful example of this period is the Bedford Hours (1423) in the British Museum. During the Middle Ages the illumination of MSS. was carried on in the scriptorium attached to every monastery. It was afterwards practised by laymen, but gradually died out after the invention of printing, lingering on in France as late as the reign of Louis XIV.
Click for more about Harleian