Ink Sac is a black dye item dropped 1-3 per kill by Squids in Minecraft, added in Beta 1.2.
Guide
Locate a Squid in any river, ocean, or lake; Squids spawn at any light level in Java Edition.
Bring a sword or trident; a Looting III sword raises the maximum drop to 6 Ink Sacs per Squid.
Hit the Squid until it dies; it drops 1-3 Ink Sacs onto the water surface or seabed.
Swim to the floating Ink Sac items quickly before they despawn after 5 minutes.
Use 1 Ink Sac to make Black Dye, or combine 1 Ink Sac + 1 feather + 1 book to craft Book and Quill.
Wandering Traders sometimes sell 3 Ink Sacs for 1 emerald, a safe alternative if you cannot find a Squid.
Squids spawn in rivers, oceans, and most water bodies. On Java Edition they spawn at any light level; on Bedrock Edition they require light level 0-7.
Place 1 Ink Sac, 1 feather, and 1 book anywhere on the 3x3 crafting grid. The recipe is shapeless and yields one Book and Quill.
Yes. Placing 1 Ink Sac in any crafting slot produces 1 Black Dye. Ink Sac itself also works as a direct black dye on wool, beds, candles, banners, and glass.
Yes. Squids continually respawn in water, so Ink Sac is fully renewable on both Java and Bedrock Editions.
Yes. Wandering Traders sometimes offer a trade of 3 Ink Sacs for 1 emerald, available on both Java and Bedrock Editions.
The item ID is minecraft:ink_sac. The item was added in Beta 1.2 in January 2011 and exists in both Java and Bedrock Editions.