The basic painting techniques used by the artists of Ajanta to create the caves’ lustrous kaleidoscopes of colour changed little over the eight centuries the site was in use, from 200 BC to 650 AD. First, the rough stone surfaces were primed with a thick coating of paste made from clay, cow-dung, animal hair and vegetable fibre. Next, a finer layer of smooth white lime was applied. Before this was dry, the artists quickly sketched the outlines of their pictures using red cinnabar, which they then filled in with an undercoat of terre-verte. The pigments, all derived from natural water-soluble substances (kaolin chalk for white, lamp soot for black, glauconite for green, ochre for yellow and imported lapis lazuli for blue), were thickened with glue and added only after the undercoat was completely dry. Thus the Ajanta paintings are not, strictly speaking, frescoes (always executed on damp surfaces), but tempera. Finally, once dry, the murals were painstakingly polished with a smooth stone to bring out their natural sheen. The artists’ only sources of light were oil-lamps and sunshine reflected into the caves by metal mirrors and pools of water (the external courtyards were flooded expressly for this purpose), a constraint that makes their extraordinary mastery of line, perspective and shading – which endow Ajanta’s paintings with their characteristic otherworldly light – all the more remarkable.