At the beginning of the 13th century, the bai glass industry in Italy was particularly developed, especially the glass produced in the city of Venezia is well-known in the world. In 1317, when they tried to make colored glass in Zhuan, they accidentally discovered that the addition of manganese dioxide would make the turbid liquid glass clear, and thus invented transparent glass.
With transparent glass, glass craftsmen began to explore ways to make mirrors from glass. They first grind the metal plate to be flat and smooth, then combine it with glass to try to make a glass mirror. It was really good when it was just finished, and it was bright and clean. But before long, the portrait in the mirror became blurred. It turns out that this is because moisture and air have penetrated through the very fine gap between the metal and the glass, and the metal plate has been oxidized. Later, they began to melt various metals and pour them on the glass, hoping to combine with the glass to make a mirror, but they all failed.
In 1508, the Italian glass craftsmen Dal Carlo brothers finally developed a practical glass mirror. They first put tin foil on the glass surface, and then poured mercury. Mercury is a liquid metal that can dissolve tin well. Then, a thin layer of tin and mercury alloy (called "tin amalgam") is formed on the glass. "), this kind of tin amalgam has high power and can adhere tightly to the glass to become a real mirror.
However, the ability of mirrors coated with mercury to reflect light is not very strong. It takes time to make, and mercury is poisonous, so it was later eliminated. Nowadays, mirrors have a thin layer of silver on the back. This layer of silver is not coated. There is no electroplating, it is coated by the chemical "silver mirror reaction". Add glucose water to the ammonia solution of silver nitrate. The glucose reduces the invisible silver ions into silver particles, which are deposited on the glass to make a silver mirror. , And then apply another coat of paint. The shiny thing on the back of the mirror is not mercury, but silver.
In recent years, many mirrors in department stores have been plated with aluminum on the back. Aluminum is a shiny silver-white metal, which is much cheaper than precious silver. To manufacture aluminum mirrors, aluminum is evaporated in a vacuum, and aluminum vapor is condensed in On the glass surface, it becomes a thin aluminum film, which is shining. This kind of aluminum mirror is cheap and good, and it is very promising.