An alloy of copper and tin used to make mirrors, especially formerly for telescopes.
- ‘The composition is 7 of tin to 22 of copper, melted twice over, as in speculum metal, to secure a perfect alloy.’
- ‘They were made of low-reflectivity speculum metal - a copper - tin alloy containing 45 percent tin.’
- ‘At first he tried to follow Newton's advice and make glass mirrors back-coated with a tin-mercury amalgam, but he soon switched to speculum metal.’
- ‘The original mirror, currently on display in Liverpool Museum, was cast in speculum metal, a special alloy of copper and tin.’
- ‘They are now made by ruling, with a diamond-point, a polished surface, such as glass or speculum metal.’
We take a look at several popular, though confusing, punctuation marks.