MATERIAL SCIENCE APPROACH TO THE TECHNOLOGY OF MINTING "PROOF" QUALITY COINS. STUDY OF SILVER ALLOYS STRUCTURE AND IMPROVEMENT OF MIRROR SURFACE QUALITY ON COINS
There are issues of coins made of precious metals for collection and investment purposes. Coins are divided into two main groups according to their mintage process: 1) those executed in "proof" quality; 2) those executed in regular "uncirculated" quality or improved "diamond-ancirculated" quality.The Pruf mintage is the highest quality of minted coins and is achieved by means of special machines and special ways of minting tools.The proof technology includes several pressings of the mint stamp on the same surface of the coin billet on the minting presses, developing a pressure of hundreds of tons on the tool. The proof quality coins have a perfectly flat, mirror-like surface of the field and, as a rule, a matted relief pattern contrasting with it. The relief must be clear, with the finest details clearly visible. Such coins have, as a rule, a complex composition, multidimensional picture. There should be no scratches, notches, burrs or the smallest irregularities of the field surface (e.g. wavy or orange peel-like areas) visible to the naked eye on the coins.In order to prevent the "orange peel" defect, a method of macro- and micro-analysis of the structure of the original silver alloy ingot and a method of alloying the ingot with beryllium were developed.