Question about polarizing lense/invisible message

[kristapsr]

Hi guys!

I would appreciate your help for this short question.

So I am building an escape room (more info in wiki - real life escape rooms)

and I basically want to use polarizing lenses to hide a message.

I would have a photo frame with a message in it and 2 layers of polarizing lenses on top of each other. in front of the message.

I have been given to understand that by twisting the upper polarizing lense you can make the glass impossible to see though or vice verca if you twist the upper lense the other way.

This effect is shown in this video.

(at 1:50 minute mark)

My question is this. Since I am a beginner in field of optics, what kind of lenses should I buy to make my idea possible? (I am also on a pretty strict budget, could you please also write down the average price?)

And if I have mixed somethign up, I hope I expalined my idea clearly, and someone can explain how I can achieve this "invisible message if the lenses are rotated in the wrong way" effect?

Thank you very much!

[swansont]

You an find cheap polarizing sheets (not lenses) on the internet. For example

http://www.polarization.com/polarshop/

http://www.edmundoptics.com/optics/polarizers/linear-polarizers/visible-linear-polarizing-laminated-film/45669/

or here

 

The problem for a hidden message is that these will block part of visible light, so if this is backlit, the "hidden message" will still be visible, unless it's set among parts that have similar transmission, and the pattern can be hidden.

 

such as

http://makezine.com/projects/spy-tech-polarized-hidden-messages/

 

It's also possible to do this with "color reveal" systems

http://photonicswiki.org/index.php?title=Basic_Optics_-_Outreach_Kit#Color_filters