Lightly wet the Flash Paper or Cotton with no less than 25% pure water. Keep it in a cool, dry place - or in the freezer.
Flash products have a shelf life of about 1 year. After that time it is best to dispose of it safely as it can expire.
If the flash product seems to be taking on a strange color (Yellowing or a rust-like color) be sure to dispose of it as it may self-ignite if it expires.