Minieco has a fun secret message valentine that she spruced up using a bottle and cut out confetti hearts. The secret is lemon juice. Using a paint brush or even a q-tip write the secret message on a blank piece of paper. To reveal the secret message the recipient must heat it using an iron, light bulb or heater.
Small hands big art cuts up the secret message and stuffs them into a homemade heart shaped and laced up transparent envelope.
Get the instructions here:
http://www.smallhandsbigart.com/blog/featured-article/semi-secret-valentine/