Palomo, A., M. Blanco-Várela, P. Herrero, and N. Prendes. “Rupestral Paintings of the "La Graja" Cave. Pigment Characterization and Digital Image Analysis”. Materiales De Construcción, vol. 54, no. 273, Mar. 2004, pp. 57-72, doi:10.3989/mc.2004.v54.i273.223.