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Blue #1 / Aogami #1 Steel
About Blue #1 Steel in Japanese Knives
Blue #1 steel, widely recognized among aficionados of Japanese knives, has various names that might be confusing for beginners. Known primarily as Aogami #1, where "aogami" translates to "blue" in Japanese, it's also referred to as blue paper #1. Contrary to what some might believe, the name does not derive from the color of the steel itself; rather, it comes from the tradition of wrapping the steel in blue-colored paper.
In the industry, this steel might also be found labeled as (Blue) 1 (YSS), Ao-Ko, or Ao-ichi-ko. In this nomenclature, "ichi" means "one" and "ko" stands for steel in Japanese. This type of steel is a high carbon steel produced by Hitachi, containing 1.3%-1.4% carbon, making it very pure with very low phosphorus (<= 0.025%) and sulfur (<= 0.004%) content. It is specifically developed for crafting tools and knives, prized for its quality and performance.