History and What It Became

The philosophical egg is one of the most consistently illustrated vessels in the whole alchemical corpus, appearing across medieval and early modern manuscripts as the sealed container in which the entire work, the ordered sequence of blackening, whitening and reddening stages, was believed to take place from start to finish. Its alternate name carries the more lasting legacy: the technique of sealing the vessel completely airtight was attributed by tradition to Hermes Trismegistus, the legendary founding figure of the whole hermetic corpus, and the vessel sealed this way was called the vas hermeticum, "the hermetic vessel." That attribution is a traditional one rather than a documented historical claim about any real sealing method Hermes Trismegistus personally invented, since Hermes Trismegistus is himself a legendary rather than a historically verifiable figure.

What survives from it is entirely linguistic rather than physical: seventeenth-century English writers began using "hermetic" to describe anything sealed or secret, and "hermetically sealed" passed from alchemical jargon into completely ordinary English, used today for anything from a jar of preserves to a spacecraft door, almost always by someone with no idea the phrase started with a sealed glass egg on an alchemist's furnace.