speculum metal

noun
1.
any of several bronze alloys with a high tin content, often containing other materials, as silver, brass, lead, zinc, or arsenic, used for making mirrors and reflectors.
Also called speculum, speculum alloy.
Origin
1790-1800
British Dictionary definitions for speculum metal

speculum metal

noun
1.
a white hard brittle corrosion-resistant alloy of copper (55–70 per cent) and tin with smaller amounts of other metals. It takes a high polish and is used for mirrors, lamp reflectors, ornamental ware, etc