[@AlexStarsion] They're called demacite, and the easiest explanation is that it's a more common practice, so the use of demacite ink and sigils is...not as common as crystal use, but maybe it helps specify the desired effect?  Focus it?

My real concern is whether Amune would have heard of using ink and sigils, or whether she'd be forced to conclude Zander is a Magi right off.  Not that it will probably take her long to find out, but I imagine the "feel" of magic cast with crystals and the feel of magic used by a Magi directly is different.