Ink Sac

Ink sacs are items dropped by squid. They are used to create black dye.

Squids
Squids drop 1–3 ink sacs upon death.

Fishing
Ink sacs can be obtained as a "junk" item from fishing.

Compound creation
Ink sacs can be created from its base elements, using the compound creator.

Trading
Wandering traders sell 3 ink sacs for an emerald.

Trading
Journeyman-level Librarian villagers have a $2/3$ chance to buy 5 ink sacs for an emerald in Java Edition, and will always offer the trade in Bedrock Edition.

ID
In Bedrock Edition, ink sacs have the ID name  with data value 0.