How do u or they make one way glass

Can u make it at home from normal glass?

There is no such thing as a true one-way glass. That is, there is no substance or device which allows light to pass in only one direction. If there was, you could make a “light motel” (light will come in but it won’t check out). You can leave it in your room and it will absorb light, getting hotter and hotter. That violates the laws of thermodynamics.

The “one-way glass” you see on TV (and, I presume, in real police stations and such) are just glass with a mostly reflective, and slightly transparent, coating. You attach that between two rooms and turn off the light in one room. From the bright room, the glass looks like a simple mirror. Some light would come from the other room if it was lit, but it is not. From the dark room, there is very little reflection, and most of what you see is light transmitted through the glass from the bright room.

“u” can make it "ur"self.

Take 2 pieces of regular window glass and sandwich about 15 layers of very thin polyethylene film (from a drycleaners bag) between them.

Make sure the side you’re on is darker than the other side.

A few years ago I saw a minute or two on CNN about some security technology show. One item they featured was one way bulletproof glass. It looked like a thick sheet of plexiglass but bullets would go through one way, but not the other. Am I remembering this correctly? And if so, how the f*ck did they do that?


What’s normally called one way glass" is artially aluminized glass. If you’re on the darker side, then the erson looking in from the more brightly lit side won’t see you. If the stick a flashlight against the glass, though, they’ll be able to see you. (Arthur C. Clarke had his hero do this in the novel “Childhood’s End”)

As for whether it’s possible to make an optical device that will pass light one way but not the other – it is. The only such “optical diode” I know is the Faraday Rotator. It’s a magneto-optical effect tha rotaes the plane of polarization of linearly polarized light differen ways for different directions of propagation (as opposed to most other polarization-sensitive devices that operate the same ay in either direction). Sandwich one of these between crossed polarizers and you can build a device that will ony ransmit light in one direction. They use it in inertial confinement “laser fusion” devices like SHIVA and OMEGA to prevent reflections from the target and lenses from going back through the amplifier banks nd destroying them.

…just a few short months ago, I quit my job with one of the worlds largest glass manufacturers. Let’s say the companies name rhymes with “Bilkington,” but in the State, it used to be, or rhyme with “Fibby-Lowens-Ord” or LOF or something…

The type of glass you are speaking about is a front-surface coated glass, rather than the traditional rear-surface “silvering.” The difference being that as you look at the glass, the reflective surface is directly on top, illiminating the paralax error (the image shift) and giving the added benefit of allowing a person to veiw through the glass at the person facing it. They can do this in secrecy provided they are not in a well lighted room themsleves.

Rear-view mirrors are made this way as are some high-end bathroom mirrors. Some incorporate a electro-resistant coating, which is used in the auto industry for self-dimming mirrors. Pretty cool, actually and quite a mark-up.

The actual glass used, to answer your question, is normal clear glass. Usually. The glass you see on sky-scrapers…same thing, essentially. We…they used blue, bronze, grey and silver on various colored glass to get different characteristics.

FWIW: In addition to the coating giving the mirrored affect, it often added thermal charcteristics to the glass. Again, quite a mark-up, but them this stuff is pretty amazing and the coating process is pretty involved.

Useless info that’s probably wrong:

You can tell if someone’s got a one-way mirror on you and you don’t have a flashlight by touching a pen or something to the mirror. If the tip of the pen in the reflection in the mirror touches the tip of the pen you’re holding, then it’s one-way. If there’s a space between the two, then it’s a normal mirror (and this is because of the thickness of the glass or something, I don’t really know).

At least, this is what I read somewhere…It could be totally wrong. I encounter surprisingly few one-way mirrors to test it out on in my day to day life, heh.

  • Tsugumo

Your gut was right. It’s wrong.

An added benifit of top- or ront-coated glass is that it does not degrade the way “silvered” mirrors will. If you’ve seen an old mirror that has “splotches” or discoloration marks throughout, it is usually do to to introduction of air and moisture tot he coated surface, and oxidation of the silvering material.

Front-coated glass does not have this problem because te glass is coated while still very hot (in the 1,000 degree F range) and the coating chemicals actually bond into the glass surface. Even light scratching will not remove the coating, as opposed to the surface coating used in the older, and cheaper silvering.

Hi Jayshah. One way glass, often termed a ‘one way mirror’ is semi-silvered glass in between two rooms - one brightly lit and the other dark. From the lit side it’s a mirror. From the dark side it’s a window.

You can make something very similar for yourself.

Go to your friendly neightbourhood car accessories store, and buy yourself a DIY “Sun Screen” window kit. You also need a photo frame. The finished ‘mirror’ will be the size of this photo frame.

Back at home, open the photo frame. Toss the cardboard backing, you don’t need it. Take out the glass, and lay it on something clean and flat. Take your DIY sunscreen material, and cut out a piece one quarter inch bigger than the frame on all four sides. Clean the top side of teh glass, leaving it clean and dry. The sun screen stuff comes with a protective backing layer. Peel this back at the corner. Press the exposed corner of the sunscreen film on to the glass with the reflective side up. Then just gradually work your way down, peeling off the backing sheet, and pressing the sun screen stuff on to the glass. The aim is to get it flat and smooth, no bumps. For a final smoothing process, work from the middle outwards. GO away and leave it to dry overnight.

Cut away any excess sun screen and put the ‘mirrored’ glass in the frame. Hang this in front of your spy hole. Make the spy hole MUCH smaller than the frame (3 x 3 inches is fine) and NOT at eye level. With your new mirror in place, keep the room on the viewing side completely dark. Done.

Just one comment, ianzin, it’s a two-way mirror. One-way mirrors are what almost everyone already has: you look in and there is a reflection, and that is the extent of it’s use. It’s not possible to veiw through the rear of this type of glass for reasons mentioned in my previous post (the opaque silvering process), hence one-way. :smiley:

Other than that, yeah, you could probably follow those directions to make it at home. Buyer Beware, though.