speculum metal

American  

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.

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speculum metal British  

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

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Etymology

Origin of speculum metal

First recorded in 1790–1800

Example Sentences

Thus all risk of contractile tension, which is so dangerously eminent and inherent in the case of sand-mould castings, made of so exceedingly brittle an alloy as that of speculum metal, is entirely avoided.

From James Nasmyth: Engineer; an autobiography by Smiles, Samuel

L. M. Rutherfurd introduced into common use the reflection grating, finding that speculum metal was less trying than glass to the diamond point, upon the permanence of which so much depends.

From Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 4 "Diameter" to "Dinarchus" by Various

But speculum metal is a material of a very intractable description.

From Great Astronomers by Ball, Robert S. (Robert Stawell), Sir

It is employed pure for numerous purposes, and is also mixed with other metals to form bell metal, speculum metal, for optical purposes, and German silver.

From The Mines and its Wonders by Kingston, William Henry Giles

For speculum metal when cold is excessively brittle, and were the casting permitted to cool like an ordinary copper or iron casting, the mirror would inevitably fly into pieces.

From Great Astronomers by Ball, Robert S. (Robert Stawell), Sir