We report the self-assembly of aligned arrays of silver nanoparticles governed by a reaction–diffusion–precipitation process. The average 2 μm wide bands containing nanoparticles which are ∼160 nm in diameter are highly periodic with ∼0.9–3 μm spacing. Morphological and analytical characterization of the particles has provided crucial information for the formulation of a series of reactions explaining the band formation. We propose that the silver/silver oxide colloids in the bands turn into elemental silver particles upon UV illumination.