An optical conoscopy study of a reentrant discotic nematic-Biaxial nematic phase transition

► Conoscopic images near the discotic nematic-biaxial nematic-discotic nematic phase transitions are reported. ► The optical sign (positive) of these nematic phases is also determined. ► The biaxial nematic phase appears clearly as an intermediate phase between two discotic nematic phases. ► The occurrence of a reentrant discotic nematic-biaxial nematic phase transition is optically characterized.