Welcome to brain Stuff from How Stuff Works. 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. They're 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 metall exalt, which can be dissolved in liquid and sprayed onto the glass in a process called silver ring. 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 silvering, 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 testimeror to see if it's translucent, block the light around you and try to peer through A bright flashlight can help illuminate any thing that might be behind that mirror. Check out the brainstuff channel on YouTube, and for more on this and thousands of other topics, visit how stuff works dot com.