What is the recipe for silly putty?
4 teaspoons of any kind of glue.
5 spoonfulls of starch.
2 drops of food coloring.
No, it does not harden! It is always playable, even if you forget it on your desktop. The only way to harden silly putty would be to expose it to extremely cold temperatures. For example, Silly Putty hardens when put into liquid Nitrogen. It will harden the putty, but it will regain its texture as soon as it warms up.