Ink Sac

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

Squid
Squid drop 1–3 ink sacs upon death.

Fishing
10 Ink sacs can be obtained as a "junk" item from fishing. Luck of the Sea decreases the chance.

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.

Crafting ingredient
$$, ink sacs can be also used in banner patterns:

Dye

 * Each type of dark prismarine can be crafted using varying amounts of 8 prismarine shards.

Trading
Journeyman-level Librarian villagers have a $2/3$ chance to buy 5 ink sacs for an emerald $$. They always offer the trade $$.

ID
Java Edition:

Bedrock Edition:

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