Hello, Sorry if this has been asked before but I can't turn up any information. I'd like to start mixing film and paper developers and need some rough idea about the shelf life of individual ingredients in powdered form. I'll probably start with D76 and Defender-55. I'll purchase the chemicals from Artcraft. He ships in either plastic jars or plastic bags, depending on the quantity. I imagine these are all exposed to air when he fills the order. Also, containers are not full. Thanks in advance. -Paul B.