Coin silver is an alloy of 90% Silver and 10% copper. It was the alloy used in most of the Americas as they had no reliable domestic source of silver for silversmiths to work from. When  silversmiths needed raw materials, they often had to buy and melt existing silver objects (including coins) to make objects for clients. Peruvian and Bolivian silver of the 18th and 19th century is notoriously high quality .