^ what people said about about the jars and airtightness

Also, you'll be able to tell if it is moldy. It'll have a lot of white dust and spores on it and it'll have a crappy smell. It smells nothing like weed, and looks disgusting, so you should always be able to tell. Still though it is smart to keep mold in mind when you're hitting a blunt with unknown origins. I've read that you can get lung infections and serious illnesses from smoking moldy bud.