I hand coat these glass vials and jars internally with a cutting edge mirror chrome finish, causing the interior to be fully reflective.
Mirrored containers such as boxes are used to trap bad people and situations with their own energies and to bounce those back at them indefinitely.
Boxes are great - extremely effective at feeding someone their own toxicity, negative energy and even black magic, but they're a bit more work than anyone likes and it's not easy to get those mirrors installed without catching your own reflection and thereby at least exposing yourself and at worst putting yourself in the trap.
The inner geometry of the bottle makes it so you actually have to try pretty hard to catch your reflection accidentally, and gives a fun house mirror effect to the little world inside.
The large and medium jars seal simply with the included mirrored lid, and for the small vials I recommend just sticking a black candle in the neck and burning it down to seal the vessel.
Mirrored vessels can also be used by more experienced practitioners for catching (and trapping) spirits, and for scrying/divination.