Chemicals that have properties between those of conventional liquids and solid crystals. Orientation of the crystal-like structure of the chemicals results in optically variable effects. Cholesteric liquid crystals have two refractive indices, a property known as birefringence (the ability to rotate the polarisation of incoming light and reflect circularly polarised light either clockwise or anticlockwise). Liquid crystal technology is used for security features that are validated with a polarisng filter.