A week spent at Japanese swordsmith Manabe Sumihira’s helping out with the operation of his tatara. Manabe chose to operate a pig iron smelting zuku-oshi tatara instead of the more commonly known kera-oshi.
The pig iron decarburizing process can be seen here (in Japanese, click on various links): http://www.eonet.ne.jp/~sumihira/19sageba/00sage/00sage%20.html
More details are available on these pages:
Home-made steel: A week at Manabe Sumihira’s Zuku-oshi Tatara
The Sumihira Zuku-oshi Tatara