An investigation of paint from a mural in the church of Sainte Madeleine, Manas, France.

The pigment in brown paint samples taken from a church in the Drôme region of France has been shown to be almost pure 6-bromoindigo and 6,6'-dibromoindigo. The composition of the pigment was established by comparison with 6-bromoindigo and 6,6'-dibromoindigo standards using atmospheric pressure photoionization combined with liquid chromatography and tandem mass spectrometry. The brown paint samples were taken from a frieze of ca 20 brown images having symmetric tree-like forms composed of five overlapping filled circles representing foliage. The tree-like images, simple rather than artistic, had a metallic luster. The molar ratio of 6-bromoindigo and 6,6'-dibromoindigo in the brown paint pigment (98:2) is remarkably similar to that of shellfish purple from the Mediterranean Murex brandaris (96.5:3.5) thus, it is possible that the origin of the indigoid compounds in the brown paint pigment is the eastern coast of the Mediterranean Sea. As the production of Tyrian purple ended with the fall of Byzantium in 1453, purple pigment had to have been produced prior to this time. We have conjectured about the circumstances that may account for the use of 'purple' in this manner in the Drôme region and how the pigment was transported there from the eastern coast of the Mediterranean Sea during the time of the Crusades.