A chemical reaction that shows a periodic colour change between magenta and blue with a period of about one minute.

Occurs with a mixture of sulphuric acid, potassium bromate (V), cerium sulphate, and propanedioic acid.

The colour change is caused by alternating oxidation-reduction in which cerium changes its oxidation state (Ce³⁺ gives a magenta solution while Ce⁴⁺ gives a blue solution).