What is "arsenical bronze"

n. a natural alloy of tin consisting of a small amount of arsenic, of a better quality than pure copper.

Arsenical bronze is an alloy in which arsenic is added to copper as opposed to, or in addition to tin or other constituent metals, to make bronze. The use of arsenic with copper, either as the secondary constituent or with another component such as tin, results in a stronger final product and better casting behaviour.

Since copper ore is often naturally contaminated with arsenic, the term "arsenical bronze" when used in archaeology is typically only applied to alloys with an arsenic content higher than 1% by weight, in order to distinguish it from potentially accidental additions of arsenic.