Speculum metal
Encyclopedia : S : SP : SPE : Speculum metal
Speculum metal is a very hard white alloy of four parts copper to one part tin, or according to other sources, 67% copper and 33% tin; some compositions contained 1–2% of arsenic. Composition with 45% tin has more resistance to tarnishing.
It was used by some early telescope makers. For instance, Lord Rosse in 1845 used the alloy for the 72-inch mirror of his "Leviathan of Parsonstown" telescope. The metal has the unfortunate property of tarnishing rapidly, requiring constant re-polishing.
Use of speculum metals for mirrors declined after 1859, when Leon Foucault published his results on silvered glass parabolical mirrors.
See also
External links
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.