Indian Head gold pieces was modified by Barber, was "worthy of J.J. Audubon". Dies for the half eagle were sent to the mints in Denver and San Francisco; both western mints reported difficulties in striking the new pieces. Landis wrote to his counterparts at the other mints, advising them that the planchets, or blanks, needed to be shaved very slightly to strike properly. The new coins proved to be thinner than earlier coins of their denomination, due to the field being raised above the design. This meant that automated sorting machines could not reliably sort them when mixed with earlier coins. The new gold
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