Blue #1 steel has several different names which can confuse people that are just getting into Japanese knives. It is called Aogami #1 (aogami translates to blue) and it also can be called blue paper #1. Some people think that the blue is the color of the steel but this is not true. The steel has been wrapped in blue colored paper for decades and this is why it's called blue. (Blue) 1 (YSS) - Also referred as Ao-Ko, or Ao-ichi-ko, where ichi is one in Japanese and ko is steel. Hitachi high carbon steel(C 1.3%-1.4%), very pure(P <= 0.025%, S <= 0.004%) specifically developed for tools and knives. Ref - Aogami 1 Steel Composition. In my experience - very good steel, and very popular choice for high end Japanese kitchen knives. A lot of Japanese custom makers use it. Takes very fine edge, and holds it long time. Easy to sharpen, even at 65HRC. Slightly better wear resistance compared to Aogami(Blue) 2, however slightly less tough compared to it. I have several kitchen knives in this steel: Watanabe Honyaki Gyuto, Nakiri and others. Takes patina easily, but just wiping it clean during cutting and washing after using it, prevents rust completely.