Addition of base improves the homogeneity of aqueous copper amine complex preservatives injected into wood. The base includes at least a portion of alkali metal hydroxides, alkali metal carbonates, alkali metal phosphates, alkali metal borates, and/or alkali metal pyrophosphates, the corrosivity of the composition to steel and galvanized steel is reduced, and the leach rate of the copper from the wood is also reduced.