Question

how is a plane mirror made ?​

Answer 1

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Plane mirrors are made by putting a thin layer of silver nitrate or aluminium behind a flat piece of glass

@Badgirl

Answer 2

Answer:

An aluminium glass mirror is made of a float glass manufactured using vacuum coating, i.e. aluminium powder is evaporated (or "sputtered") onto the exposed surface of the glass in a vacuum chamber and then coated with two or more layers of waterproof protective paint.