So what causes silver to stick to glass on the back of a mirror?
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Be aware that modern mirrors use aluminium because it’s cheaper and less prone to tarnishing than silver. Even so, the process is sometimes still called silvering even though aluminising is more accurate. The glass is placed in a vacuum chamber with aluminium which is heated to a high temperature. Some of the metal evaporates and then condenses in a layer on the glass.
Sorry, I don’t have an answer for what mechanism creates the adhesion between the aluminium and glass, although it’s more robust than that between silver and glass. Apparently chromium is even better and has sometimes been used as an undercoat with aluminium on top.
It’s actually made there. Mirrors are made using a chemical solution that contains dissolved silver (or sometimes other metals), and then they perform a chemical reaction which causes the silver metal to come out of solution. When it does, a thin film of it will stick to any surface it can find.
[Here’s a video of the whole process done in a small lab setup](https://youtu.be/hUX_cpFWNso). It’s not a process you should try yourself at home -the video goes into the problems with doing that- but it shows the basics of how it all works.
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