While the Zalt family has existed for 10 generations, their history stretches back much further. They were known as witches and sorcerers before contact with Coxish explorers, in which their practice was officially given the name necromancy. The Zalt family itself was established as a way to prevent their practices from being lost thanks to the new Coxish influence. They've operated both openly and in secret over the years, depending on the political climate and the tolerance for their practice.
They hold the belief that there are two types of energy in the world, the potential for life and the potential for death. Necromancy is manipulating the death energy to the user's advantage to bring back dead corpses and inflict sickness on opponents.
Two factors effect the given power of a necromancer: however many near death experience they've had in the past and their current health. The less healthy a necromancer is, the more powerful they are. They trade physical power for magical.
The family is rather well known for having an open door policy on teaching new apprentices, as long as they are willing to sign over their corpse when they die. Several die sooner than expected due to the harsh training process, leaving one out of every 10 apprentices able to actually survive their training. They require at least one near death experience at the family's hands in order to teach their apprentices how to harness the energy. It usually takes at least 3 near death experience before they can get the hang of it enough to animate somethign dead, 5 to get the hang of using that same energy to inflict illness.
No one knows if the process itself is what creates more powerful necromancers or if it's a powerful person who can survive the process. No universities or science groups want to be the ones attributing to finding out.