The short time ion bombardment during ion milling resulted in a dramatic change in the surface composition of alpha-brass, selectively removing up to 2/3 of the Zn atoms during the first 5 to 10 minutes of ion milling. This differential sputtering occurred at various ion beam energies and at target temperatures as low as −196°C (LN2 temperature). The effect of differential sputtering completely disappeared after ion milling times in excess of three hours. Such a dramatic change in composition could not be attributed either to a difference in sputtering yield or to different ion milling conditions. It was shown that under constant ion milling conditions this differential sputtering depends strongly and only on the condition of the foil surface. The unexpected disappearance of the effect of differential sputtering with time was attributed to stabilization of a characteristic surface topography produced by long time ion bombardment.