Crystal structure studies of selected lithol red salts with the use of powder diffraction data

Lithol reds - azo compounds used as pigments in paintings and in the plastics and printing industries - were studied, with the result that the crystal structures of their salts with NH4+ and Na+ cations were determined from powder diffraction data. Moreover, the thermal stability and light-induced degradation of lithol reds were investigated. The obtained results were correlated with the disappearance of colours in the paintings of Mark Rothko.