Iga region, where this donabe is made, used to be the bed of Lake Biwa about 4 million years ago. The clay from this region is naturally highly heat-resistant and has been used for open-flame cooking for many hundreds of years. This clay consists of a high level of pre-historic fossilized microorganisms that leave the clay porous when fired. The porous body gives the donabe remarkable heat-retention ability. The donabe gradually builds the heat when it’s heated, then it cools down very slowly after the heat is turned off. This, along with the glaze that promotes the far infrared rays (FIR – the same effect as how the glowing charcoal cook ingredients without direct flame) when it’s heated, allow the donabe to produce a gentle, steady heat that penetrates to the core of each ingredient. The effect is ingredients are cooked evenly with all the flavors sealed inside.