Tamahagane (Lit. Jewel Steel) is a millennia-old tradition using iron sands sintered together in a clay charcoal furnace called a Tatara. The furnace is used only once before being disassembled to retrieve this precious steel. Today, very few tatara exist, and most of the steel they produce is reserved for traditional katana forging.
The small amount of steel that reaches the kitchen knife market is sold exclusively to master blade-smiths, making it one of the world's rarest steels. The sintering process closely resembles modern powdered metallurgy, which means that—while not stainless—this steel should outperform other Japanese high carbon steels.