The well‐known difficulties with preparation, handling, and mounting of thin foils are avoided by the use of aluminum oxide foils (25 to 250 &mgr;g/cm2, or 700 to 7000 A thickness) which are grown on a solid piece of mechanically shaped aluminum that serves also as the necessary robust frame. These foils have excellent properties for an application in the spectroscopy of particle and quantum radiation. A simple method for the mechanical and chemical preparation will be described. The foils are gas tight, smooth, and withstand a considerable pressure. A formula describes the relation between breaking pressure, diameter, and thickness for circular shaped foils.