A benchtop, one-step, maskless-but-parallel method of etching micropatterns is described. Transparent conducting oxides and semiconductors are etched with lateral resolution down to 200nm using a reaction-diffusion process. Patterned hydrogel stamps act as a reservoir and a two-way "pump" transporting etchant onto the substrate while removing reaction products into its bulk. This low-cost method is suitable for rapid rototyping of bulk and thin film materials, minimizing the need for multistep lithographic processing.