the uniformity of the surface activity may be investigated, and any "hotspots" of photoactivity identified. By varying the composition of a semiconductor photocatalyst surface across the surface itself, a paii photoactivity surface map may be used to determine the optimal composition which yields the greatest photocatalytic response. The rapid colour change of paiis makes them suitable for such applications as: Quality control (in laboratory, factory and on site); Marketing; Counterfeit identification; Research material assessment. See also Photocatalysis Self-cleaning glass References Photochemistry Catalysis Articles containing video clips