Scanning confocal microscopy of experimental active film (section ‘Experiments’). Plus-half defects are marked as green comet-shaped symbols and minus-half defects by dark blue trefoil-shaped symbols (section ‘Defect analysis’). The zero-isolines of the Q criterion are shown as solid lines coloured by the handedness of the enclosed vortex: red for clockwise and blue for anticlockwise (section ‘ Q criterion’). Scale bar, 100 m.
