You've probably heard the story of Hua Mulan substituting for her father in the army. In the "Ode to Hua Mulan", there are lines like "arranging her cloud-like hair at the window, and applying flower-yellow makeup in the mirror". Mirrors have existed in China for a long time. However, these were not the mirrors we use today. The earliest "mirrors" were naturally water surfaces. In ancient times, people wanted to see what they looked like and whether they were dirty, so they would look at calm water. Therefore, since ancient times, there has been the saying that "the water is as smooth as a mirror". Later, bronze mirrors were invented - by polishing the surface of bronze, they could also reflect light very well. The mirror used by Hua Mulan was a bronze mirror. In the past, there were craftsmen shouting "grind mirrors, grind mirrors" in the streets and alleys, who used grindstones to grind bronze mirrors for people. This was because bronze mirrors had a drawback: if they were left in the air for too long, they would easily oxidize and become gray on the surface.
Bronze mirrors were, of course, far inferior to today's glass mirrors: in glass mirrors, you can clearly see yourself without any flaw, but in bronze mirrors, you can only see a blurry shadow. Glass mirrors are shiny all over. So what was coated on the back of them? Some say it was mercury, while others say it was silver. Who is right? Both are right! In the earliest glass mirrors, mercury was coated on the glass, because mercury could dissolve tin and turn into a viscous silver-white liquid - tin-mercury amalgam. This tin-mercury amalgam could tightly adhere to the glass and become a mirror. However, making such mirrors was very time-consuming, taking a whole month to complete.
Later glass mirrors were made by coating a very thin layer of silver on the glass. This silver was coated using a special and interesting chemical reaction - the "silver mirror reaction". The so-called "silver mirror reaction" is to use glucose solution as a reducing agent. The aldehyde group in sugar can reduce the silver in silver nitrate to metallic silver, which precipitates on the glass surface.
The glass used to make mirrors must also be very smooth. If the mirror surface is not smooth, when you look at it, hahaha, your face will be crooked and distorted. There is a kind of funhouse mirror that is deliberately made with concave or convex glass.
The manufacture of mirrors doesn't seem very complicated, but when people first started making mirrors with the "silver mirror reaction" more than 300 years ago, it was quite a challenge! Because the mirrors made at that time were just like a piece of deer skin: the silver layer on the glass was uneven, with patches here and there. Some places had silver, while others had none at all. Why was this? It turned out that the technology of making mirrors, especially the silver mirror reaction, was still a secret in the mirror-making industry at that time, and mirror makers would never easily tell others this secret. Now, this method is no longer a secret - the key is whether the glass is washed very clean. If there is a little oil stain on the glass, the newly reduced silver can't be deposited and won't be coated. Now, in mirror factories, the glass is carefully washed with a 1/10000 solution of acidic stibine chloride, then rinsed with distilled water several times, and finally dried with an electric furnace. To make the mirror durable, a layer of red protective varnish is usually applied after silver coating. In this way, the silver layer becomes even harder to peel off.
Some people think that the back of mirrors is coated with mercury, and if it gets on their hands and is eaten, they will be poisoned. In fact, this concern is outdated. Almost all the mirrors used now are coated with silver. You can only encounter mercury-coated mirrors in museums nowadays.
Aluminum mirrors
Nowadays, silver mirrorsIt has been replaced by a new type of glass mirror—the inexpensive aluminum mirror. This is achieved by "plating" a very thin layer of aluminum metal on the back of the glass using a vacuum coating method.