To smelt zinc:
You will need zinc ore (you can mine this), rock salt (minable), coal (minable) or charcoal (you can buy
this), some retorts (sold near the distinlation furnace for 23 dinars or findable in treasure - thanks again Quinlax),
a reed stick (foragable in the duck marsh near Thebes - thanks for the info Quinlax), and a room with a distillation furnace
(north of the building at the entrance to the mining area).
First you need to SMELT ZINC INGOT FROM ZINC ORE.
You'll need to prepare your ore by JOINING your ORE WITH some CHARCOAL/COAL to get some powder. You
may need to mix in more coal or charcoal.
Now you need to mix in some rock salt by JOINing your POWDER WITH some SALT.
Next you need to make pellets, so ROLL your POWDER.
Now PUT your PELLETS IN your RETORTS.
Once you have your reed stick, PUT your REED STICK IN your RETORTS.
CLOSE your RETORTS to keep any air out.
Now you need to put the RETORTS IN the FURNACE and then LIGHT the RETORTS once you have them loaded in the
Next you'll need to STOKE the RETORTS (you might have to add IN FURNACE).
When that's done, just GET your RETORTS FROM the FURNACE, and you're done!