GLASS

A furnace turns sand or red sand into it, one for one. Breaking a placed one back out needs Silk Touch. Sand sits at the surface of nearly every beach and desert in the game, a furnace is one of the first blocks anyone places, and the smelt itself takes moments. Almost nothing on this site is cheaper to make than glass is, which makes buying it look like the wrong move before you have even checked the price.

The case for the Librarian shows up underground and away from sand. Deep in a cave system with no furnace lit and no beach for a day's walk, an emerald for a stack of panes is faster than backtracking to the surface twice, once for sand and once for fuel.

It also sits at his cheapest tier, journeyman, which is why glass tends to be the first thing a new librarian offers once he has anything worth buying at all.

One seller. The Librarian hands over 4 glass for 1 emerald once he reaches journeyman, a rate fixed in the trade file rather than rolled inside a range, so no amount of shopping around finds a better price from a second librarian.

No villager buys glass back off you. Panes and bottles you craft from it never return any value at a trading post, so the only emeralds glass ever touches are the ones spent buying it.

Glass sells for as little as 1 emerald for 4 at a time, from the Librarian at the Journeyman tier, and nothing else on the list costs less. The price is fixed rather than rolled, so a second Librarian will quote you exactly the same.

The Librarian at its journeyman tier asks 1 emerald for 4 glass. 8 of the 72 villagers that pay emeralds, emptied out:

a dark oak boat against 26 potatoes for the same 1 emerald, 26 times the carrying, and the shortest wait is the Butcher at 37.5 real seconds of shelf, gathering not counted.

Any unemployed villager standing near a lectern becomes a librarian, and reaching journeyman is a short climb from the tier he starts at, not a long one. Glass tends to show up early precisely because that tier is easy to reach.

Once open, the slot hands over 12 rounds of glass before it locks, and a restock brings the same offer back rather than swapping it for something new. Break his lectern before he settles the job and the whole shelf, glass included, disappears with it.

12 rounds clear the slot, and the librarian needs 2 real minutes at his lectern before it opens again. A Minecraft day runs 20 real minutes, room enough for two of those refills.

Stand there a full day and he sells 24 rounds of glass, which is a lot of panes for very little real time, faster than a furnace would smelt the equivalent stack of sand even with fuel already lit.

Skip the trade whenever a furnace is in reach. Sand smelts one for one and the fuel cost is a fraction of an emerald, so this row only wins on convenience, never on price.

The same Librarian buys books at 4 an emerald, so selling him a stack on the way in covers a good part of what the glass costs on the way out.

Also on the Librarian's list: book and quill, clock, compass, yellow candle, red candle, and paper, the rest of one lectern's shelf.

Glass is one sand in a furnace, one block out. Breaking it gives you nothing at all unless the pickaxe has Silk Touch, which makes a glass wall one of the few builds where a mistake costs the material rather than a minute.

It goes a long way if you cut it. Six blocks on the grid give sixteen panes, so a window made of panes uses well under half the glass of one made of blocks, and panes join up into a frame by themselves.

Three glass also make three bottles, which is where potions start. A brewing setup quietly eats more glass than most windows do.