GLASS BOTTLE

A Cleric at expert buys 9 glass bottles for 1 emerald, the same villager whose own brewing stand is built entirely around turning potions into and out of this exact container.

A crafting grid makes 3 at a time from 3 glass, a near one-for-one swap that leaves nothing wasted. It has a second source that costs nothing to craft: witches drop it too, so a fight that was already happening for their other loot can leave a stray bottle or two behind as well.

Bring 9 glass bottles to a Cleric who has reached Expert, and he pays 1 emerald back. No other villager profession touches glass bottle at any tier, buying or selling.

The best rate any villager offers is an emerald per 9 glass bottles, from the Cleric, and 3 of the other 5 pay out faster. No villager sells glass bottle back, so it is emeralds out and nothing in.

One slot at the Cleric takes 9 glass bottles a trade, 12 trades, 12 emeralds. 8 of the 72 villagers that pay emeralds, emptied out:

12 acacia boats against 384 rotten flesh for the same 12 emeralds, 32 times the carrying, and the shortest wait is the Fisherman at 7.5 real minutes of shelf, gathering not counted. Glass Bottle itself pays 9 an emerald, so 29 of the 72 ask less and 41 ask more.

A brewing stand claims any unemployed villager right away, but glass bottle sits deep on the Cleric's sheet. He needs 150 trade experience banked before expert unlocks, level 4 of five, several rounds of earlier trades away from a fresh hire.

Once open, the slot takes 9 bottles a time, 12 times before it locks, and a villager restocks at most twice a Minecraft day. Being deep on his sheet does not change that schedule once it is unlocked.

12 sales close the slot, and the wait after that runs 2 real minutes flat, no faster no matter how quickly the trades are clicked through. Two of those refills fit inside one Minecraft day, itself 20 real minutes long.

Worked that hard, one Cleric clears 216 glass bottles for 24 emeralds across a single day, a modest side income next to whatever else his brewing-stand sheet is paying out.

One trip, one restock: the Cleric takes 108 glass bottles across 12 trades before the slot locks, paying out 12 emeralds total. Empty bottles saved from potion brewing count just as well as freshly crafted ones.

Where they go back: that Cleric also sells redstone dust, his cheapest offer going the other direction.

Also on the Cleric's list: ender pearl, nether wart, bottle o' enchanting, rotten flesh, gold ingot and lapis lazuli.

Three glass make three bottles, and every potion in the game starts as a bottle of water. That is why the Cleric collects them: his own workstation is a brewing stand, and a stand runs on bottles the way a furnace runs on fuel.

Bottles also hold honey and experience. A bottle of honey clears poison and refills hunger, and a bottle of enchanting thrown on the ground gives experience directly, which is the only way to buy levels rather than earn them.

A bottle does more than hold potions. Used on a full beehive it takes honey, which is food that also clears poison, and three honey bottles make a honey block.

In the end, a bottle swept through the ender dragon's breath attack fills with dragon's breath, and that is the only way to make a lingering potion. No other item collects it.

Filling one at a cauldron works when there is no water in reach, which is the whole reason a cauldron is worth building in the nether.

The Cleric takes 9 Glass Bottles per emerald. You can blow them yourself at one bottle per block of glass, or let witches drop them: How to Build a Witch Farm in Minecraft collects Glass Bottles along with the redstone and glowstone.