I - ( You know... ) I'm actually not sure about the mechanics. I'm sure it's a mix of everything. The stele that they're drawn onto the skin with is made from Adamas -- it's a heavenly metal. That, combined with the meanings the angel has taught in the Grey Book - which is the book of runes that have existed for as long as Shadowhunters have - create the power, I suppose. Well. Once they're drawn on the intended object. Usually Shadowhunter skin. And I guess our angelic blood is what makes them work for us. The ones that appear to me -- Um... It's kind of a long story, actually. And not exactly fun.