The study and development of permanent hair dyeing, agent especially about the new harmless ones such as iron salt, plant extracting and Melanin hair dyeing agent are reviewed.

综述了永久性染发剂的研究开发，尤其新型无毒染发剂如铁盐染发剂，植物萃取物染发剂和黑色素类染发剂等。

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In the Middle Ages it was discovered to be a rich source of aluminium sulphate - a crucial raw material used as a fixing agent in dyeing cloth.

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