Britannia silver is an alloy of silver containing 11 ozt 10 dwt (i.e. 11+1⁄2 troy ounces) silver in the pound troy, equivalent to 23⁄24, or 95.833% by weight (mass) silver, the rest usually being copper.
This standard was introduced in England by Act of Parliament in 1697 to replace sterling silver (92.5% silver) as the obligatory standard for items of "wrought plate". The lion passant gardant hallmark denoting sterling was replaced with "the figure of a woman commonly called Britannia", and the leopard's head mark of the Worshipful Company of Goldsmiths (in London) replaced with a "lion's head erased".