The people in my setting (urban fantasy, starting in 1998 America and moving forward) have a bit of an engineering dilemma they need to work out regarding potionmaking. The magical substances they brew with have a notorious tendency to degrade within an hour after collection unless properly stored. They have specially-made flasks for this purpose, made out of a metal with the ability to hold these magical ingredients in proper stasis as long as the liquid is completely encased in the metal on all sides in an airtight seal, with no air getting in the way of the liquid's complete encasement in the metal.
For the potions they brew, normal flask designs work just fine for this. Fill the bottle carefully all the way to the top and then carefully screw it tight, then drink the whole thing when you're ready to use it.
For storing the ingredients, however, this serves more of a problem, because unless they too are all used at once every time they're opened, the half-empty contents can't properly be kept in stasis unless the insides are "watered down" to make the flask full again, which would be dizzying and frustrating to keep track of when using the leftovers for the next potion. It would be ideal if the ingredients were kept in some manner of container, made out of this aforementioned metal, which was somehow adaptive or adjustable and could provide an airless, airtight seal to the contents inside even when the container isn't at full capacity.
I can't even imagine what such a container would look like, but if such a design exists, naturally the people of my setting would have had the incentive, time and resources to invent it, so I need to make sure it actually doesn't exist before I start having it be an actual obstacle my characters need to deal with. So I thought I'd ask around here:
Is there any way to design a metal container so that even when the container isn't filled to capacity, it can still be sealed with just liquid, and no air, inside of it?