<P> The earliest mirrors were made from polished obsidian during the Stone Age . By the Bronze Age most cultures had adopted mirrors made from polished discs of bronze, copper or other metals . Such metal mirrors remained the norm through to Greco - Roman Antiquity and throughout the Middle Ages in Europe . In the 1st century CE glass mirrors began to appear, now believed to have originated in Sidon in present - day Lebanon . Ptolemaic Egypt had manufactured small glass mirrors backed by lead, tin, or antimony . In the early 10th century, the Persian scientist al - Razi described ways of silvering and gilding in a book on alchemy, but this was not done for the purpose of making mirrors . </P> <P> From the 15th century to 1900, tin - mercury amalgam was used in European mirror manufacture . The thin tinfoil used to silver mirrors was known as "tain". </P> <P> In 1835 German chemist Justus von Liebig developed a process for depositing silver on the rear surface of a piece of glass; this technique gained wide acceptance after Liebig improved it in 1856 . The process was further refined and made easier by French chemist Tony Petitjean (1857). This reaction is a variation of the Tollens' reagent for aldehydes . A diamminesilver (I) solution is mixed with a sugar and sprayed onto the glass surface . The sugar is oxidized by silver (I), which is itself reduced to silver (0), i.e. elemental silver, and deposited onto the glass . </P> <P> In 1856 - 57 Karl August von Steinheil and Léon Foucault introduced the process of depositing an ultra-thin layer of silver on the front surface of a piece of glass, making the first optical - quality first surface glass mirrors, replacing the use of speculum metal mirrors in reflecting telescopes . These techniques soon became standard for technical equipment . </P>

When did scientists learn how to put silver on glass
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