WEBVTT - How do one-way mirrors work?

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<v Speaker 1>Welcome to brain Stuff from How Stuff Works. Hey, I'm

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<v Speaker 1>Christian Sager. This is brain stuff, and today we're talking

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<v Speaker 1>about one way mirrors a K A two way mirrors

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<v Speaker 1>a K A half silvered mirrors a K. Transparent mirrors

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<v Speaker 1>a K A security mirrors a K. Surveillance mirrors a

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<v Speaker 1>K A observatoor tron's I don't I don't know if

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<v Speaker 1>that last one is a real thing. You know those

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<v Speaker 1>things that you see in crime dramas when one cop

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<v Speaker 1>is interrogating a suspect while another one watches through a

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<v Speaker 1>window that appears from the suspects side to be a mirror.

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<v Speaker 1>That is not magic. TV cops aren't wizards and transparent mirrors.

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<v Speaker 1>They're science. A regular old mirror, the kind hanging over

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<v Speaker 1>your bathroom sink. That's a sheet of glass holding up

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<v Speaker 1>an extremely thin layer of reflective metal, and I mean thin,

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<v Speaker 1>It's less than a micron thin. The metal comes in

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<v Speaker 1>the form of a metall exalt, which can be dissolved

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<v Speaker 1>in liquid and sprayed onto the glass in a process

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<v Speaker 1>called silver ring. That's because silver, in the form of

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<v Speaker 1>silver nitrate, was the first stuff used for this process.

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<v Speaker 1>These days, most mirrors are actually silvered with aluminum, which

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<v Speaker 1>is cheaper and sturdier, and once it dries, the reflective

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<v Speaker 1>layer is given an opaque backing to first of all

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<v Speaker 1>protect it from scratches, and then to stop any light

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<v Speaker 1>that manages to dodge through the metal layer. Without this backing,

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<v Speaker 1>you'd be able to faintly see the wall behind it. See,

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<v Speaker 1>photons are tricky, and mirrors they're not perfect. But what

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<v Speaker 1>if you purposely make a mirror imperfect. Manufacturers of translucent

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<v Speaker 1>mirrors spray and even thinner, more sparse layer of silvering

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<v Speaker 1>onto the glass, meaning it reflects less light. For example,

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<v Speaker 1>let's say half the light of an ordinary mirror, and okay,

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<v Speaker 1>a little light gets absorbed by the silvering, but the

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<v Speaker 1>rest passes straight through the glass like it's a window,

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<v Speaker 1>which it is. A translucent mirror is just a reflective window,

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<v Speaker 1>and it's a window from both sides. Depending on the

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<v Speaker 1>manufacturing process. It might be slightly more reflective from one side,

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<v Speaker 1>but you can look through it from either. So how

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<v Speaker 1>come the suspect sees his reflection but the cop sees

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<v Speaker 1>the suspect. Well, it's just a trick of the light.

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<v Speaker 1>The observer's room is kept dark while the observes room

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<v Speaker 1>is lit up very bright, so on the cop side

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<v Speaker 1>more light is coming through the glass than being reflected

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<v Speaker 1>from the room, and from the suspects side, more light

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<v Speaker 1>is reflecting from the room than being transmitted through the glass.

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<v Speaker 1>And hey, people ask about this a lot. If you

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<v Speaker 1>ever want to testimeror to see if it's translucent, block

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<v Speaker 1>the light around you and try to peer through A

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<v Speaker 1>bright flashlight can help illuminate any thing that might be

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<v Speaker 1>behind that mirror. Check out the brainstuff channel on YouTube,

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<v Speaker 1>and for more on this and thousands of other topics,

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<v Speaker 1>visit how stuff works dot com.