"This iron was found in the stronghold of the Mother of Invention, experimenter for the Winter Court. She had a stash of iron in her labs - a mix of rough blades, and smaller fragments, for testing on the mortals and changelings in her charge."

A polite way of saying, the people that MoI had kidnapped and changed so they'd also be more vulnerable to the metal. The idea that mortals might deserve any agency or respect from the fae's still too much of a sticking point between the Summer monarchs to be worth harping on.

"This wasn't a single piece," Beau instead emphasizes, "found by chance, for some idle curiosity. This was a collection, intentionally gathered over time, for reasons I can only assume were nefarious."

She glances towards the others, those with more scientific background and those with the stored memory, for backup.