Indirect method

…In China, cast iron was refined, decarbonized, and turned into wrought iron. Thus, in contrast to the direct process of iron ore → wrought iron, a two-step process (indirect process) of iron ore → cast iron → wrought iron developed in China. They also developed a technology to melt wrought iron, which has low carbon content, into cast iron, which has high carbon content, to make iron with a carbon content between the two, that is, steel. …

*Some of the terminology explanations that mention the "indirect method" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…中国では鋳鉄を精錬して脱炭し錬鉄に変えた。こうして鉄鉱石→錬鉄という直接法に対し鉄鉱石→鋳鉄→錬鉄という二段階法(間接法)が中国で発展した。また炭素の多い鋳鉄に炭素の少ない錬鉄を溶け合わさせて両者の中間の炭素の鉄，すなわち鋼にする技術も生まれた。…

※「間接法」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報