A trade

Smelter

Melts various ores into usable ingot form.

Where it works

Its bench

Each of these is a station an owner places on their land. What you can make depends on standing in front of one.

Smelts ore into ingots and blows glass from sand — five metals, thirteen bottles, and a melt you do not come back for within a day is lost.

18 of ours

The other eleven

A trade that cannot make its own inputs buys them, which is the whole economy in one sentence.