My story is set in the late 90s USA, revolving around a secret society of mythical humanoids. Almost every species humanity has ever thought was real is real, or at least used to be before going extinct. Due to their eternal youth, they are collectively referred to as immortals.
A central aspect of the magic system in my setting is that nearly all things magical are tied to organic life. Nearly every living creature produces magical energy in some form, regardless of whether or not it's a form they can actually use. Magic that influences things outside of a living creature has a very short half-life and must usually be continuously supplied energy by the user of the magical ability.
Initially there was an exception to this rule, however, called a soul gem. Whenever an immortal dies, they leave behind a bead-sized magical gem that possesses their race's magic in a usable form. This is a crucial centerpiece in enchanting objects, potion making, etc. Initially they were conceived as an outright exception to the rule, a seemingly-infinite engine of magic that could sustain a magical effect indefinitely in an inanimate object. However, since I didn't like how utterly out-of-place this characteristic was in my magic system, this has changed.
The way soul gems are currently envisioned, they're described as essentially crystallized MANA (the magical equivalent of DNA). They aren't a source of magical energy in and of themselves. However, like light through warped or colored glass, magical energy that passes through them can be changed in form and effect, which is why they can be used to make weapons or clothing express the gem's racial powers, or why rings inset with soul gems can grant certain forms of that race's abilities to other magical creatures... but crucially, only when they are supplied with magical energy by the being who is touching them.
This works well for those purposes, but there was another thing that soul gems were supposed to do that I'm having trouble rationalizing under the new explanation of what they are: their role in potion-making.
Potions are a real thing, and to explain why -- despite potion brewing not requiring the brewer themself to be a magically-active being -- the magical properties of the ingredients haven't been observed by the scientific community, soul gems are crucial in the process. You take magical ingredients, namely the specific parts of plants and organs of animals that contain magical energy (newts only have magic in their eyes, for example), and you cook the magical ingredients and dip a soul gem into them when they're heated, the specific soul gem influencing the potion's effects. That still works under the "like light through glass" analogy. The magic comes from elsewhere, the gem simply changes its form.
The issue is that under room temperature, another thing soul gems are supposed to do is keep potion ingredients magically fresh despite the plants and animals the ingredients came from obviously no longer being alive. The idea is you "pickle" the ingredients in a liquid solution, and then drop a soul gem, any soul gem, into that liquid solution, and as long as the gem is touching the solution the ingredients are in, they will keep their magical energy. The same applies to finished potions, they need to have a soul gem kept in the bottle and kept in contact with the liquid to keep the effect alive until they're ready to be used. But now that soul gems don't actually generate any magical energy of their own, I have difficulty imagining how I could justify this.
Why would a gem that warps and shapes magical energy, rather than generating it, do anything to keep the magical energy in potion ingredients fresh longer?