Make a blast furnace in minecraft - how?

it's also the armorer's job block. put one in a village and a jobless villager will claim it, and once you've levelled an armorer up they sell diamond armour, which beats any amount of faster smelting.

5 iron ingots, 1 furnace, 3 smooth stone. iron across the top, iron / furnace / iron in the middle, smooth stone along the bottom. the smooth stone is what stops people. cobblestone in a furnace gives you plain stone, and you have to smelt that stone a second time to get smooth stone. regular stone won't fit the recipe.