Short and Quick Answer
An aluminium glass mirror is made of a float glass manufactured using vacuum coating. Vacuum coating is the deposition of a film or a coating in a vacuum (or low-pressure plasma) environment. For instance, aluminium powder is sputtered (“spray”) onto the exposed surface of the glass in a vacuum chamber and then coated with two or more layers of waterproof protective paint.
Far from being a personal cosmetic accessory, mirrors in Mesoamerica were divinatory aids and also formed a part of the elite status costume. The use of mirrors in Mesoamerican culture was associated with the idea that they served as portals to a realm that could be seen but not interacted with.
The earliest man-made mirrors were from polished stone and mirrors made from black volcanic glass obsidian.
In late Postclassic (c.1200–1521) obsidian came to be the stone of preference for fashioning mirrors in Central Mexico. They used polished obsidian as a reflective surface.
Eventually, they started to produce more sophisticated mirrors made of copper, bronze, silver, gold and even lead.
Contemporary mirrors did not come into being until the late Middle Ages, and even then their manufacture was difficult and expensive. One of the problems involved was the fact that the sand used for glassmaking contained too many impurities to produce real clarity. It wasn’t until the Renaissance when the Florentines invented a process for making low-temperature lead backing, that modern mirrors made their debut.