speculum metal


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speculum metal

n
(Metallurgy) 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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Speculum metal is much heavier than glass and tarnishes quickly, and mirrors required frequent repolishing.
This fully functioning recreation of Sir Isaac Newton's reflecting telescope features a 70-mm f/4 primary mirror (made of glass rather than the speculum metal that Newton used), and a tube wrapped in waxed parchment paper.