Fragment of furnace wall and vitrified lining. The orange material is the clay wall of a shaft furnace which has been fired at temperatures over 1000C. The glassy green material is a mixture of impurities from the iron being smelted mixing with impurities in the clay and vitrifying with the heat. The small rounded curve is part of the hole in the side of the furnace where the nozzle from the bellows (tuyere) would be inserted.