Mirror metal

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Mirror metal (also Latin speculum 'mirror') is a very hard, easily polished, whitish bronze alloy made of copper, tin and additives of other metals that improve hardness and polishability.

Alloys

Some alloys used for mirrors are:

  • simple tin bronzes made of copper and tin in a mixing ratio of 4: 1 to 2: 1, sometimes with the addition of 1 to 2% arsenic
  • 71–72% copper, 18–19% tin, 4–4.5% antimony and lead (old Roman mirror)
  • 80.8% copper, 9.1% lead, 8.4% antimony (a Chinese metal mirror)
  • Platinum and steel in a ratio of 1: 1 (results in a particularly white metal)
  • 350 parts copper, 165 parts tin, 20 parts zinc, 10 parts arsenic, 60 parts platinum

use

Due to the good polishability, metal mirrors (speculum) can be made from the alloy; it was even used to make the main mirrors of telescopes . For example, Lord Rosse used this alloy in 1845 to manufacture the “ Leviathan ” mirror, which is 1.8 meters tall and weighs 3.5 tons .

The disadvantage of the alloy was that it started to tarnish comparatively quickly in air and so the reflectivity decreased; Constant polishing of the mirrors was necessary. Metal mirrors were replaced by silver-plated glass mirrors, which were developed by Carl August von Steinheil and Léon Foucault , based on a method by Justus Liebig in 1859.

Web links

Commons : Spiegelmetall  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d mirror metal . In: Meyers Konversations-Lexikon . 4th edition. Volume 15, Verlag des Bibliographisches Institut, Leipzig / Vienna 1885–1892, pp. 138–138.