proof dies 上市 Deposited
Those speciall burnished and otherwise prepared for making proof coins. Because the coins are not annealed between impressions, they become stress-hardened and wear down the dies more rapidly than do production coins. The Mint Bureau gave average die life (1971) for cent proof dies at 2,300 obv., 2,900 rev.; nickels, 2,500 obv., 2,300 rev.; dimes, 2,600 obv., 2,700 rev.; quarters, 1,500 (i.e. 2,500?) obv., 2,200 rev.; half dollars, 2,400 obv., 3,200 rev.; Eisenhower dollars, 2,500 obv., 3,500 rev. The corresponding figures for dies for business strikes: cents, 1,000,000 obv., 1,200,000 rev.; nickels, 170,000 obv., 185,000 rev.; dimes, 150,000 obv., 165,000 rev.; quarters, 155,000 obv., 170,000 rev.; half dollars, 150,000 obv., 180,000 rev.; Eisenhower dollars, 100,000 obv., 200,000 rev. (NSM 9/72, pp. 842-43.) Earlier figures were lower; at least as recently as 1888, some proof dies were used also for making production coins.
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