The characterization of various mixtures obtained by fractional recrystallization of sulphur-selenium melts is described. Optical absorption spectra of thin films, mass spectra, and X-ray diffraction data reveal two distinct ranges of homogeneity, the break occurring at 14 at. % Se. The optical absorption edge of crystals containing less than 14 at. % Se varies linearly with composition. A direct optical transition to the conduction band of S8 and a transition due to trapped excitons are thought to contribute to the excessive width of this absorption edge.