"then he shall write": This tells me only of ink. Whence do I derive (as also permitted) dye, rock-lichen, resin, and vitriol? From "then he shall write" — with anything.
"a scroll": This tells me only of a scroll. Whence do I derive (as also permitted) reed, nut, olive, and carob stalks? From "and he shall place it into her hand" — in any event. If so, why is it written "a scroll"? Just as a scroll is characterized by (relative) permanence, so, all things that are thus characterized (are permitted for the writing of a get) — to exclude those things which are not thus characterized. R. Yehudah b. Betheira says: Just as a scroll is characterized by being unrooted to the ground, so, all things that are thus characterized (are permitted for the writing of a get) — to exclude those things which are not thus characterized.