This method of spell preservation was created by the Incantor Larl'Olarl, who once lived in a sprawling manse on the Green Beaches of the Quell Sea. It is thought that the soundless waves of the Quell gave rise to the noise-intolerant oysters that lay buried the weird green sand.
Larl discovered that if he pried open the shell and whispered a secret or a spell between the lips of the oyster, that the sound would irritate the mollusk to such a degree that it would begin to coat the sound with nacre. Over time, a shining pearl would develop around the sound, its colour a milky transparency. When held to the eye it appeared as if the pearl was filled with slowly moving shapes like a tilted hour glass or frozen cloudstuff.
There is no way to tell what such a treasure contains until placed in the mouth. The next breath from the lungs will release the secret or the spell, said in the same tongue and voice of the original speaker.
If a pearl containing a spell is placed into the mouth of an Incantor, they may speak that spell as needed, but only that spell. Scribbled notes found in the ruins of Larl's manse have hinted that attempting to speak a different spell with the pearl still remaining on one's tongue may have consequences both dramatic and dire.
The words contained within can only be released by disolving the pearl in vinegar.