 Because of the loose nature of the sand it was difficult to smelt in a normal bloomery, or to use in a blast furnace to make pig iron, so the Japanese developed an open-topped bloomery called a tatara.The tatara was built with a low, tub-like shape, resembling a horizontal blast-furnace, into which ironsand could be poured and contained, and smelted in stages.Unlike with other methods, the charcoal was piled on top of the sand and smelted from above, keeping it from being blown about by the blasts from the bellows.