Determination of the composition and the origin of the ochre brown patina on the monumental Bab Agnaou gate (Marrakech, Morocco)

Like the majority of the Mediterranean monuments, the monumental Bab Agnaou gate is covered by a patina having an ochre brown hue. The petrological and mineralogical studies of this patina using optical microscopy, X-ray diffraction analysis, grazing incidence X-ray diffraction and electronic scan microscopy made it possible to determine its nature. It is about an artificial patina containing lime and clays, its colour is attributed to earth pigment. The experimental result and some rare historical documents made it possible to specify that the application of this patina goes back to the 1930s during the restoration work carried out at this time. © 2007 Springer-Verlag.