Quills used for spell books must withstand strong magical currents, but also be magically inert unlike wandwood.
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Lesser materials will crumble mid-spell and ruin the page, while wandwood will often apply the spell being written to the page under it.
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A Stylus of Bone is oft favored for its resilience. Knew a witch once who used a rough iron nail, said she didn't mind the burns.
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