User blog comment:HS664/The Book of Eldritch Secrets/@comment-2116776-20130807224245/@comment-2116776-20130808000144

the soul or essence is used to fuel a forge. a day at least would be required to fully complete a weapon and thats only for a highly skilled forge master. certain souls or essences are less than favorable do to certain passive abilities such as affecting mental state, physical state or just turning the user into a host. if the weapon get destroyed then the entity is released. when you ask "Such as how to trap the soul" do you mean how to extract the soul from a body or how to keep it bound to the weapon?