English Synonyms and Antonyms, by James Champlin Fernald
Alloy may be either some admixture of baser with precious metal, as for giving hardness to coin or the like, or it may be a compound or mixture of two or more metals. Adulteration, debasement, and deterioration are always used in the bad sense; admixture is neutral, and may be good or bad; alloy is commonly good in the literal sense. An excess of alloy virtually amounts to adulteration; but adulteration is now mostly restricted to articles used for food, drink, medicine, and kindred uses. In the figurative sense, as applied to character, etc., alloy is unfavorable, because there the only standard is perfection.