A one-way mirror, also known as a two-way mirror, is a mirror that allows one to see through it from one side while reflecting light like a normal mirror on the other side. One-way mirrors are commonly used in interrogation rooms, observation rooms, and other settings where it is necessary to observe people without being seen.
One-way mirrors are made by coating a sheet of glass with a thin layer of a reflective material, such as aluminum or silver. The reflective material is then coated with a thin layer of a transparent material, such as glass or plastic. The transparent material allows light to pass through it, but it also reflects some of the light back to the reflective material. This reflection creates the illusion of a mirror.