How does a one way mirror work?

Question

what material is lining one side of the glass and how is it manufactured?

Answer 1

A one way mirror is just a regular mirror, I think you mean two way mirror.

A "two-way" mirror is just a mirror with little gaps in the shiny metallic
coating. Looking through a two-way mirror is like looking through a screen
with holes much smaller than usual. Light will pass through in both
directions. You can see through in either direction. The shiny coating is
visible from the front.

When looking at the front, the reflected light is MUCH brighter than the
little that comes through from the back. As a result, you don't notice it.
The back side is colored dark and dull. Very little light gets reflected
from the back. Someone behind a two-way mirror can see through more easily.

If you turn off ALL lights on the side in front of the mirror, make it pitch
black, you will be able to see through from the front. Of course, there has
to be a light on behind the mirror. Whenever a two-way mirror is used for
spying, the room behind the mirror is kept dark. This way, there is no
light to be seep through to the front. Also, the room in front of the
mirror is usually kept bright. This makes it easier for the "spies" to see
what is happening. It also makes it harder for the "victims" to notice any
light getting through the mirror.

Answer 2

Just about everyone has seen a television show or movie in which a criminal suspect is questioned while detectives watch from behind a one-way mirror. How does a piece of glass manage to reflect light from one side while remaining clear on the other?

The secret is that it doesn't. A one-way mirror has a reflective coating applied in a very thin, sparse layer -- so thin that it's called a half-silvered surface. The name half-silvered comes from the fact that the reflective molecules coat the glass so sparsely that only about half the molecules needed to make the glass an opaque mirror are applied. At the molecular level, there are reflective molecules speckled all over the glass in an even film but only half of the glass is covered. The half-silvered surface will reflect about half the light that strikes its surface, while letting the other half go straight through. It turns out that half-silvered mirrors are also essential to many types of lasers -- see How Lasers Work for details.

Answer 3

It is just a partially reflecting mirror that lets some light leak through, though attenuated. I'd be surprised if it works with as much as 1/2 of the light getting through, but you can check that yourself. The light leak invariably goes both ways, so the trick is to make one room brightly lit, and the other room unlit (except for the light leaking through the mirror) and with dark walls. On the bright side, the light reflected from within that room, then, completely dominates anything leaking back through, so the contrast of the secret observes relative to the subject's own reflect is below the detection threshold of the human eye. On the dark side, though, The only light is that leaking through the window from the (brightly lit) subjects. And, since it's dark, the observers eyes are dilated so they can see that light clearly.

Oh yes, about your follow on question. The coating is aluminum, the same as on a normal mirror, except thinner so as to let some light through. Aluminum mirror coatings can be applied chemically by precipitation, or by evaporating the aluminum in vacuum, where it condenses on the glass.

Answer 4

From what I've seen...when a mirror broke...A mirror is simply a piece of glass that has a special paint on the other side....some silver type paint...that creates the glass to ' reflect '. Scratch that paint off and the mirror is simply a piece of glass again.