Soma-yaki (Soma ware) from Fukushima Prefecture is characterized by the ao-hibi, or blue-green crackling that covers the surface. An apple ash and sumi-kannyu glaze is used to achieve this effect. Somaware can also be recognized by the hashiri-uma, or galloping horse motif. This motif is said to have been requested by a feudal lord in the mid-1600's, to show pride in the region's ability to breed and train quality horses. Perhaps the most distinguishing design feature of Soma ware is the double-walled construction. The inner and outer pieces are thrown separately by the potter, and allowed to dry and firm for a short period. The inner piece is then mated to the outer piece. This design not only keeps the liquid inside hot, but also the outer surface cool, allowing one to easily hold the vessel.