A one-way mirror, also known as a two-way mirror, is a mirror that is partially reflective and partially transparent. This allows people on one side of the mirror to see through it, while people on the other side see a reflection. One-way mirrors are often used in interrogation rooms, police stations, and other settings where it is important to be able to observe someone without being seen.
One-way mirrors are made by coating a piece of glass with a thin layer of metal, such as aluminum or silver. The metal coating reflects some of the light that hits it, while allowing some of the light to pass through. The amount of light that is reflected and transmitted depends on the thickness of the metal coating. Thicker coatings reflect more light and transmit less light, while thinner coatings reflect less light and transmit more light.