​​What is the difference between One way mirror and Two way mirror?

A one-way mirror has reflective material on one side and is coated with translucent material on the other. It is the mirrors that we use in our bathrooms, cars, and so on. A two-way mirror is a mirror that has a reflective surface on one side and a clear surface on the other. It mimics a regular mirror, but you can see through the clear side to the side with the reflective surface. A normal bathroom mirror is a layer of glass about a quarter inch (6 mm) thick followed by about a 2 micron thick layer of silver followed by black paint. The light goes into the glass, reflects from the silver and goes back through the glass. A two way mirror usually is a quarter inch of glass, a 1 micron layer of silver and then a quarter inch of dark glass. Looking from the clear glass side, the reflection looks normal but maybe a little bit dark. If on the other side of the two way mirror is a dark room, very little light gets through the dark glass and the silver from the dark room. People outside will not notice anything other than the bright reflection from their side. In the darkened room, little is reflected because light would have to go through two layers of dark glass. However, light from the outside bright room comes through the thin silver and one layer of dark glass and those in the darkened room can see out.