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in metallurgy, an auxiliary alloy used to introduce alloying elements into liquid metal for the purpose of imparting specific properties to the metal melt (for example, fluidity) or the solidified metal (increased mechanical strength). The assimilation of an alloying element from the hardener is greater and more stable than if the element were introduced in pure form. Hardeners are produced by fusion of their components or by reduction from ores, concentrates, or oxides. In ferrous metallurgy, hardeners are distinguished from ferroalloys, which are used for both alloying and deoxidation of metals. Metals that are added to precious metals (for example, gold or silver) to impart to them the necessary properties (for example, hardness) or to reduce the cost of manufactured articles are also called hardeners. Copper and mercury are used as hardeners.