Make sure to read the Demon Idol page.

While spell books have but a faint trace of magic, scrolls contain significant magical potential – they contain readied spells! They have special requirements for preparation.

1. Scroll material¹⁾) can be purchased from settlements. Availability may vary.
2. A special quill. Feathers for these can be harvested from any creature of strange or magical nature.²⁾ It takes 1 hour to prepare a feather so that it can be used as a quill for this purpose. Feathers and quills expire after 1 year.
3. A special base, which should be giant squid sepia, giant octopus ink, or a comparable substance. If such a base is not used, the cost of secondary ingredients (below) is doubled. It takes 1 hour to prepare any ink, after which it must be left to stand for 24 hours, stirring occasionally. Unlike potion brewing, no special equipment is needed for ink manufacture. The containers and instruments needed are assumed to be kept in the character’s present lodging, and their cost and maintenance is included in the character upkeep cost. Ink expires after 1 year.
4. A special ingredient. This must be something that matches the motif of the spell, to be proposed by the player. A primary ingredient needed for the ink needed for a 1st level spell need not be of extraordinary magical potency or rarity, but must have at least some flourish to it. Perhaps it is something fairly mundane, but it was left in the strong moonlight, or was heated in a fire as the preparer chanted. Primary ingredients for mid- and high-level spells will be more difficult to obtain, as primary potion ingredients are.
5. Secondary ingredients costing 100 gp per spell level, or double that if lacking a special ink base.

If you can name something your character could have harvested from an adventure in the last year that might be used as a component in magic item manufacture, that is sufficient to make use of it. The actual harvesting is abstracted. You do not have to explicitly state that your character is collecting materials during the adventure. You need merely to recall a time your character could have done so in the last year.