Aluminum waveguides with twists, bends, and/or tapers were electroformed by electrodepositing aluminum on electropolished, copper‐plated, cadmium‐nickel‐alloy mandrels, followed by melting out the cadmium‐nickel alloy and dissolving out the copper in nitric acid solution. This is a new procedure for obtaining mirrorlike inner surfaces of electroformed articles. The aluminum walls (0.65 to 1.0 mm thick) were dense, strong, and ductile. The high‐purity aluminum electrodeposits were as hard as 138 Knoop. The plating baths consisted of a dispersion of toluene in a toluene solution of the fusion product of ethyl pyridinium bromide and aluminum chloride with methyl (butyl ether or another addition agent for improving the physical properties of the aluminum electrodeposits. The baths were used for as long as 560 amp‐hr/l (44 days) and could have been used longer if necessary.