You know what? I don’t think Jace knows the definition of magic, or using magical objects. You can draw marks with a with a stele. Historically, those marks would have been called sigils and which some have thought to be a form of magic. Now, it would be one thing if you proved that the stele, and thus the marks are form of unknown science. Now, I can see that the stele itself was a magical object that had the real magic (like with the serph blades) , but even the Shadowhunters are still passively using magic. However, with the possibility of the stele being magical themselves, the marks are actually magical and /or have magical proprieties. So Jace is a big fat hypocrite when he tries to claim that it’s just Mundanes who are obsessed with magic. Shadowhunters use marks to do everything from heal themselves to become invisible. I would like to also point out that Clare could have used this time to fill in the blanks about what exactly powers the marks themselves. She didn’t, and all we got is some strange analogy about rubber ducks instead.