Eisenhower dollar R is the letter closest to it, these changes were most likely made in an effort to improve the flow of metal as the coins were struck. In 1974 and again in 1977, the Denver Mint struck a small number of pieces on silver-clad planchets, or blanks. Both times, these came from planchets which had been shipped from the San Francisco Assay Office to Denver. The first ones in 1974 were found independently by two Las Vegas blackjack dealers. The 1974 planchets were initially intended to be used for "brown Ike" proof strikings; Mint policy then was that rejected silver
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