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We all know sunglasses make any spy look cool, but these will let you see secret messages!

This secret message project uses polarized film (technically a linear absorptive polarizer) to make our message hidden. To see the message you either have to look through a second piece of film, or put on a pair of polarized sunglasses.

How this works:

Linear polarized film has tiny lines etched into it in one direction. These lines filter the light passing thru the film, polarizing it. If you take two pieces of linear polarized film and arrange their polarization lines in the same direction, light will pass through both layers.

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If the two pieces of linear polarized film are “cross polarized”, they will block light.

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Polarized sunglasses use this effect to block glare. We can take advantage of this to build our project.

In our project we will make a mosaic of small squares of linear polarized film to spell out our secret message. The person that wants to see our hidden message needs to look through their own piece of linear polarized film or polarized sunglasses.