Isabella quarter is without distinction". The "American Journal of Numismatics" had other criticisms of the quarter: Minting of what Barber dubbed "showy quarters" began at the Philadelphia Mint on June 13, 1893, six weeks after the exposition opened. Leech had planned to strike the pieces using polished blanks, or planchets, and workers at that mint handled the coins carefully; unlike the half dollar, surviving specimens display relatively few contact marks from other coins. The first piece struck, along with numbers 400, 1,492, and 1,892, were struck in proof condition and sent to the Lady Managers along with certificates attesting to their status.
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