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Ever passed by a mirror in a curious place and wondered if it may have been a two-way mirror? Take time with this 5 minute read to protect yourself with these two-way mirror finding tips.

One way or two way mirrors refer to the same material based on what side of the glass you are observing into.

What is a two way mirror?

A glass two way mirror, also known as a one way mirror, is a semi-transparent mirror that is traditionally made for privacy and security purposes. It is made on a grey glass substrate and the mirror coating is baked on during the manufacturing process.

THE FINGERNAIL TEST

By using your fingernail and facing the front of the mirror, you can test to see which side the reflective coating is facing. This is very important. Optical mirrors are coated on the first surface of the glass as well as two way mirrors.

If your fingernails reflection touches itself that is the coated side. If there is a gap between your finger and its reflection that will be a standard mirror.

 

Standard Mirror

What is a standard mirror?

A mirror begins as clear glass. Glass panels are then transported to a washing station. Then the glass is blasted with water and serum oxide ( a powder derived from a type of earth). The glass is heavily polished with rotation brushes at the front and back surfaces removing oils and other contaminants.

The mirror coating is on the back side of a standard mirror.

The glass is then sprayed with very hot de-mineralized water. the water must be demineralized because the minerals in plain tap water would damage the metals applied next. The first metal applied is liquified tin. This will be applied to the back of the mirror. It allows the second metal, silver, to adhere. Silver does not stick directly to the glass. The silver is also in a liquid form mixed with a chemical activator. Within seconds of interacting with the tin, it hardens. You can start to see the reflection coating appear. Its the silver backing that transforms clear glass into a mirror.

The silver backing is then sealed with two coatings of paint. Paint alone is not enough to protect the backing long term. First, a layer of copper is applied, then the two coatings of paint. Lastly, an acid wash to remove any remaining metal residues. The final piece of mirror is inspected for any imperfections or air bubbles in the mirror coating.

Glass Two Way Mirror

70% reflection coating with an 11% light transmission on a dark grey substrate, glass two-way mirror cannot cheat the fingernail test. The reflection coating must be facing the room that is being observed. That way the people being observed are only seeing their reflection. On the opposite side, the darker room is located where the observer will be watching.

Notice the fingertips reflection touching itself. Very different from that of the standard mirror’s reflection.

The light is even on both sides of the mirror in this picture. You are able to see through the semi-transparent glass at the moment.

Front

Side

Back

Glass two-way mirror cannot cheat the fingernail test. The reflection coating must be facing the room that is being observed. That way the people being observed are only seeing their reflection. On the opposite side, the darker room is located where the observer will be watching.

Acrylic Two Way Mirror

70% reflective with 25% light transmission on a grey substrate, acrylic two way mirror is reflective from both sides of the substrate. Meaning it can be installed either way. If installed backwards ( the coated side on the back ) it can cheat the fingernail test looking like the reflection of a standard mirror! Something to think about if you are testing a questionable mirror. Acrylic tends to have a different feel than glass. Rubbing your nail gently across the surface may help you determine if you have found an acrylic two way mirror, or a standard glass mirror.

Acrylic two way mirror will closer match the reflection tint of a standard mirror as well. Whereas glass two way mirror tends to have a bronze tint.

Smart Mirror

Smart mirror is similar to the acrylic two way mirror in properties. It has a 70% reflection with a 25% light transmission. Its reflective from both sides of the substrate. Smart mirror can be installed backwards as well ( the coated side on the back ) it can cheat the fingernail test looking like the reflection of a standard mirror!

If you are testing a questionable mirror, smart mirror tends to have a warmer tone on the reflective coating. Observe the smart mirror on the right compared to the standard mirror reflection of the mug on the left.

STILL NEED SOME HELP?

Check out our video explaining the fingernail test for two-way mirrors.

Did you know?

Two-way mirrors are dependent upon the lighting in the room. Both sides of the mirror cannot be evenly lit for the illusion to work. The observer side of the mirror must be at least half as dark for the reflection coating on the other side to properly reflect light back at those being observed.

Can a two-way mirror be antiqued?

Don’t worry. If you see an antiqued mirror, its most likely not going to be a two way mirror. With the mirror coating missing, you would see through the transparent glass right to the other side.

More Images

Want to see samples of two way mirrors?

Visit our ORDER SAMPLES page.

CONCLUSION: Now that you are armed with knowledge, never be afraid of a sketchy looking mirrors again. Just remember the fingernail test.

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