An alloy of copper and tin used to make mirrors, especially formerly for telescopes.
- They were made of low-reflectivity speculum metal - a copper - tin alloy containing 45 percent tin.
- The composition is 7 of tin to 22 of copper, melted twice over, as in speculum metal, to secure a perfect alloy.
- They are now made by ruling, with a diamond-point, a polished surface, such as glass or speculum metal.
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