Reaction-diffusion waves; homogeneous and inhomogeneous effects

Experimental evidence for the spontaneous formation of spiral waves and crossing wave patterns for the Belousov–Zhabotinsky reaction in solution are presented. Also observed are so-called ‘lateral instabilities’ with the spontaneous deformation of circular fronts in systems of low excitability. Lateral instabilities in resin-based systems, with the redox catalyst immobilised on ion-exchange beads, and the effect of the ageing of solutions, are also reported.