Glass surfaces can be given coatings of silver that make them into mirrors.
WARNING: Perform the whole experiment in less than two hours. This is because the solution generates highly poisonous silver nitride on standing. Also, the solution will give off ammonia when heated so you'll need to do this outside, in a fume hood or in a well-ventilated area. And wash away all chemicals with lots of water.
Get one gram of silver nitrate and one gram of sodium hydroxide. Then add enough water to both to completely dissolve them. Mix them together and youll get a black precipitate of silver oxide. Then add enough ammonia to completely dissolve the silver oxide. Add four grams of sugar and mix well.
The solution will deposit silver coatings when its heated. If you heat it in a glass container it will deposit silver on the inside of the container. To deposit it onto a glass pane you can put the glass into a tray with solution and heat the tray from below. But do not let the solution boil. Boiling tears the silver off the surface.
Thin layers of silver can be wiped off with a cloth if the silver goes where you don't want it. Thicker layers can be removed by applying hydrochloric acid.
This process produces a back reflective mirror, which is what most household mirrors are.
If you need to silver larger pieces of glass, or need thicker layers, just scale up the solution.