In order to properly practice Aes, a Sentry must be in a throng, preferably a Branded one. These Prometheans will then dedicate themselves to the needs of their throngmates by protecting them from harm, finding them food and shelter, providing for their interests and entertainment, and helping them on their Pilgrimages in order to further their own. If a Sentry has or shows weaknesses, they will work to correct and strengthen them to further protect and help their friends. Purification of the body and soul is also strongly emphasised among most Sentries.
Aes appears to be a very positive Refinement, but it does have its problems. While most Prometheans who know of Aes at least appreciate the efforts of their Sentry allies, some Prometheans see them as nothing more than something to be taken advantage of, and will ally themselves with a practitioner of Aes purely for the benefits the Sentry will give them. In addition, not all Sentries develop healthy connections to their throngmates; obsession and resentment are as likely to form between a Sentry and their throng as co-operation and loyalty.
Aes is considered rare because throngs are not as common as they would appear to be. Because of this steep requirement and the fact many Prometheans never make themselves part of a Branded throng, the Refinement of Bronze is hard to learn about and even harder to practice. It is extremely unlikely for a Promethean to start out on this Refinement; however, rare cases where two Prometheans were created side-by-side do allow for this possibility.
Surprisingly, Frankensteins are the most commonly seen Prometheans on the Refinement of Bronze. Aes allows for the rare companionship a Wretched often craves, and their strength and fury make them excellent Sentries for other, weaker Prometheans. Galateids and Ulgans, however, desperately want human companionship over Promethean relationships, and so shy away from Aes.