People often underestimate the importance of proper storage of their molds. Improperly storing a mold can damage it and possibly render it unusable. 

Proper mold storage: Clean the mold cavity with a sponge and soapy water and let dry.

Cast plaster into the mold and let dry. Do not demold. You will be storing the mold with the plaster casting in it to help maintain dimensional stability.

If possible, place the mold with the casting in it in a black plastic garbage bag and seal tightly.

Place on a flat level surface. 
We’ve heard from customers that have inadvertently stored their molds with objects under them, causing the mold to permanently distort.

Store in a cool, dry environment out of ultraviolet light