Gold leaf
On the strictest definition, a manuscript is not considered "illuminated" unless one or many illuminations contained metal, normally gold leaf or shell gold paint, or at least was brushed with gold specks. Gold leaf was from the 12th century usually polished, a process known as "burnishing". The inclusion of gold alludes to many different possibilities for the text. If the text is of religious nature lettering in gold is a sign of exalting the text. In the early centuries of Christianity, “Gospel manuscripts were sometimes written entirely in gold". The gold ground style, with all or most of the background in gold, was taken from Byzantine mosaics and icons. Aside from adding rich decoration to the text, scribes during the time considered themselves to be praising God with their use of gold. Furthermore, gold was used if a patron who had commissioned a book to be written wished to display the vastness of his riches. Eventually, the addition of gold to manuscripts became so frequent, "that its value as a barometer of status with the manuscript was degraded". During this time period the price of gold had become so cheap that its inclusion in an illuminated manuscript accounted for only a tenth of the cost of production. By adding richness and depth to the manuscript, the use of gold in illuminations created pieces of art that are still valued today.