An Aegis is a type of dagger that has been forged with Angel's ichor in it.
An aegis is described as looking like a common dagger.
This type of dagger can be used to unbind the demonic Binding rune for a short period of time. These daggers also have other purposes that were not explored in the books.
- It is mentioned by Clary Fairchild that you need to have a very good reason to request an aegis from the Iron Sisters as they can get very suspicious about what you're doing with the dagger as angel blood is tough to acquire.
- Sister Magdalena stabbed Jace directly on his rune which broke the spell that caused him to be bound to Sebastian for a brief period of time.