Milled coinage in 1890. In modern practice in the United States, milling, or a milled edge, can refer to the raised edge on the coin face, applied by a special milling machine after the planchets are cut out and polished. In addition, the reeding of coins of higher value, applied by the collar holding the coin when it is stamped, can be considered part of the milled edge. Milled coinage In numismatics, the term milled coinage (also known as machine-struck coinage) is used to describe coins which are produced by some form of machine, rather than by manually hammering coin blanks between
Glass-to-metal seal dark. Oxygen-free copper has to be used if the metal comes in contact with hydrogen (e.g. in a hydrogen-filled tube or during handling in the flame). Normally, copper contains small inclusions of copper(I) oxide. Hydrogen diffuses through the metal and reacts with the oxide, reducing it to copper and yielding water. The water molecules however can not diffuse through the metal, are trapped in the location of the inclusion, and cause embrittlement. As copper bonds well to the glass, it is often used for combined glass-metal devices. The ductility of copper can be used for compensation of the thermal expansion