At the time of two study missions into the conservation problems of rupestral art in Tassili N'ajjer (Algeria), surface samples from the sheltered paintings of the Neolithic period were taken. A chemical analysis showed the presence of sulfates on a thin layer on top of the paintings, and the stratigraphic study revealed, in general, a single layer of an iron oxide base (red and yellow ochre) on the rock. See also AATA 21-2134.