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 more at Wikipedia.org...
Free Download Now!
