# Is it a 2-way glass or a 2-way mirror? **URL:** \ **Category:** Factual Questions\ **Created:** [September 25, 2005, 9:35pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377 "2005-09-25T21:35:25Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\ **Post date:** [September 25, 2005, 9:35pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/1 "2005-09-25T21:35:25Z")
It’s the type of thing you always see in movies where a prisoner is being interrogated in a small room. The people in the room see a mirror. For the people on the other side, it looks like a pane of glass. So, what’s the correct terminology? Is it 2-way glass or a 2-way mirror? ---
**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\ **Post date:** [September 25, 2005, 9:54pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/2 "2005-09-25T21:54:17Z")
Two way mirror. Of course, I don’t understand this, since it only works from one direction. But perhaps what they mean is it works in two different ways. As a mirror, and as a window. ---
**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\ **Post date:** [September 25, 2005, 10:03pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/3 "2005-09-25T22:03:32Z")
:smack: I mean to add, I’ve heard it referred to as two-way glass as well, so I’m not sure if one is more correct than the other. ---
**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\ **Post date:** [September 25, 2005, 10:09pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/4 "2005-09-25T22:09:50Z")
I’d tend to vote for “glass”. It’s a piece of glass that does two things. ---
**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\ **Post date:** [September 25, 2005, 10:22pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/5 "2005-09-25T22:22:59Z")
It’s one-way glass. Two-way glass is just a windowpane. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [September 25, 2005, 10:23pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/6 "2005-09-25T22:23:56Z")
All plain window glass is “two way” (transmissive from two sides) already; an additional distinction is unnecessary and confusing. However, plain bathroom mirrors are only “one-way” (reflective only); a mirror that can function as reflective from one side, and transmissive from the other, needs the additional descriptor, “two-way”. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [September 25, 2005, 10:26pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/7 "2005-09-25T22:26:26Z")
> [@RealityChuck](#): > > It’s one-way glass. I would accept this as well. Two-way mirror, or one-way glass. ---
**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\ **Post date:** [September 25, 2005, 10:32pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/8 "2005-09-25T22:32:49Z")
Bi-glassual? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [September 25, 2005, 11:22pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/9 "2005-09-25T23:22:21Z")
> [@Fear Itself](#): > > …a mirror that can function as reflective from one side, and transmissive from the other, needs the additional descriptor, “two-way”. This is a bit of a misleading description. So-called “two-way mirrors” will actually work in either direction, depending on the relative lighting conditions on each side. The people on the side with less ambient light can see through the mirror more easily than those on the side with brighter ambient light. If the lighting conditions are reversed, so is the direction of clearest viewing. These mirrors are coated with a thin layer of reflective material that is partially transparent. The lower the percentage of light the coating lets through, the greater the reflectivity, but the larger the difference in lightning needs to exist in order for it to work. ---
**Author:** ![Speaker\_for\_the\_Dead](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@Speaker\_for\_the\_Dead](https://boards.straightdope.com/u/Speaker_for_the_Dead)\ **Post date:** [September 25, 2005, 11:58pm UTC](https://boards.straightdope.com/t/is-it-a-2-way-glass-or-a-2-way-mirror/323377/10 "2005-09-25T23:58:25Z")
Thanks, **Q.E.D.** , I’d always wondered how they worked.