Copper on silica catalysts have been prepared using ion-exchange of [Cu(NH3)4]2+ with silanol sites under basic conditions (normally pH 11). Equilibrium saturation was reached within minutes. Upon washing in distilled water or dilute ammonia at pH 7-9, dissolved Cu2+-ions, present in the interstitial particle volumes, were precipitated as Cu(OH)2 and retained in the catalyst. The solid then contained two different copper species, i.e., ion-exchanged Cu2+ and precipitated Cu(OH)2, the proportions of which varied depending on the preparation conditions. The relative amounts of ion-exchanged copper were high if preparation was based on low Cu2+ concentrations in the preparation solutions and extensive washing in dilute ammonia at pH 11 (copper loadings below 1 wt%). Copper contents between 2 and 6 wt%, obtained by impregnation at pH 11 and washing in distilled water, resulted in the presence of ion exchanged and bulk copper species. At higher loadings the ion exchanged species were a negligible fraction of the exposed copper, possibly due to coverage by bulk copper deposits. The precipitated species is concentrated in very small clusters (<5 nm) as expressed by the substantial copper metal surface in the reduced catalysts. The latter was measured by a modified nitrous oxide decomposition pulse chromatographic method.