The Blast Furnace is a building.
upgrade => Blast Furnace II
This building is an improvement of the Great Forge. It therefore requires the latter to be built.
The creation of the Blast Furnace is only possible if the technology Blast Furnace has been enabled in the province.
This building requires 36500 man-days
The construction of the building requires 3 political points, 8,000 gold, 20 wood, 30 iron and 20 tools.
This buildings allows you to stock more iron (400 instead of 200) and tools (400 instead of 200).
The Blast Furnace has a 20% improved production of the manufactoring of tools over the Great Forge.