Welcome to brain Stuff from How Stuff Works. Hi, brain Stuff, Lauren foke obam here, I've got a classic brain Stuff episode for you today, performed by our previous host, Christian Sagar, and written by me. In this one, I wanted to find out how one way mirrors work. Christian will explain. Hey,
I'm Christian Sager. This is brain Stuff, and today we're talking about one way mirrors a K A two way mirrors, a K A half silvered mirrors, a K, transparent mirrors, a K A security mirrors, a K surveillance mirrors, a K A observatoor tron's I don't I don't know if that last one is a real thing. You know those things that you see in crime dramas when one cop is interrogating a suspect while another one watches through a window that appears from the suspects side to be a
mirror That is not magic. TV cops aren't wizards, and transparent mirrors their science. A regular old mirror, the kind hanging over your bathroom sink. That's a sheet of glass holding up an extremely thin layer of reflective metal. And I mean thin, It's less than a micron thin. The metal comes in the form of a metallic salt, which can be dissolved in liquid and sprayed onto the glass in a process called silver ing. That's because silver in the form of silver nitrate, was the first stuff used
for this process. These days, most mirrors are actually silvered with aluminum, which is cheaper and sturdier, and once it dries, the reflective layer is given an opaque backing to first of all protect it from scratches and then to stop any light that manages to dodge through the metal layer. Without this backing, you'd be able to faintly see the wall behind it. See. Photons are tricky, and mirrors they're not perfect. But what if you purposely make a mirror imperfect.
Manufacturers of translucent mirrors spray and even thinner, more sparse layer of silvering onto the glass, meaning it reflects less light. For example, let's say half the light of an ordinary mirror, and okay, a little light gets absorbed by the silver ring, but the rest passes straight through the glass like it's a window, which it is. A translucent mirror is just a reflective window, and it's a window from both sides.
Depending on the manufacturing process, it might be slightly more reflective from one side, but you can look through it from either. So how come the suspect sees his reflection but the cop sees the suspect. Well, it's just a trick of the light. The observer's room is kept dark while the observes room is lit up very bright, So on the cop side, more light is coming through the glass than being reflected from the room, and from the suspects side, more light is reflecting from the room than
being transmitted through the glass. And hey, people ask about this a lot. If you ever want to test a mirror to see if it's translucent, block the light around you and try to peer through a bright flashlight can help illuminate anything that might be behind that mirror. Today's episode was produced by Tyler Clang. I'm realizing as I'm going through these how many times I worked references to
wizards into my scripts. For a visual description of how one way mirrors work, check out the video version of this episode on YouTube, and of course, for lots more completely translucent topics, visit our home planet, how stuff Works dot com.