Pigments—the palette of organic colourants in wall paintings

The present contribution deals with the use of organic colourants in wall paintings, polychrome pottery and painted stone artworks, i.e. painted artworks on inorganic supports. The term organic colourants is referred to the chemical nature of these compounds but not to the way of application; therefore, organic colourants can be dyes, lakes or pigments. The use of organic colourants in wall paintings has been given little attention in the past, perhaps on the assumption that they were rarely used by ancient artists. Recent diagnostic studies, however, brought evidence that their use was not fragmentary; on the contrary, there seems to be continuity in the centuries, at least with regard to the most widely used such as madder, Tyrian purple and indigo. Sources, alteration phenomena, identification methods and analytical evidence is given for the main organic colourants with concern to red, yellow, green, purple and blue hues. Drawbacks and issues are discussed with concern to the identification techniques.