Hello:
 
I'm Umesh a graphic designer who has a lot of interest in mixing
science and art. I am designing an invitation for a 25th Wedding
Anniversary Party. The Theme/Message I want to get across is for
happiness all it takes is a little "chemistry"....
 

What I need is to have a container that can be filled with a colored
solution (chemical). This solution should have a nice deep/rich color.
In this container I will fix a glass slide on which my inviation is
printed. The printing will be done in the exact same color as of the
solution, this will make it completely unreadable and near invisible.

WHat I require is that when this container is removed from the box
(when received by the guest) it should change from color to clear
inside 30 seconds. The mechanism that can be used to change this color
are:

1) A small electric current is passed through the solution (with a
attached battery or something) to make it clear. When the battery
supply is cut off, it should return to its color again. This should
cycle on/off for atleast a couple of hundered times and should work
for atleast two months (The invites will be shipped one month in
advance)

2) The chemical can be sensitive to light and changes from color to
colorless when it comes in contact with ambient light
(sunlight,fluroscent,incadescent), it should not require any special
light. The object being however receives it, it should work in normal
conditions day or night, indoor or outdoor (obviously i don't mean a
no moon night outdoors at normal conditions)

What is not acceptable is any form of additon required to change the
color to to start of a clock reaction. No form of heating should be
needed. It should have any chemicals that are dangerous/hazardous or
toxic in nature in case the container breaks and the guest/children
come in accidental contact with the solution.

Am real keen on this and am running out of time. Any ideas????

 
Regards,
Umesh