So I just bought a Kobayashi Seikon Dojo nakiri, Blue #2 core clad in low carbon steel. My only other carbon knife is a Hiromoto AS petty that I forced a patina on right away. I tried forcing a patina on the Kobayashi using mustard, raw beef, and lemon juice, and it really hasn't done anything. The mustard just left some slight markings. Is Blue #2 less reactive than most carbons? Even less than AS apparently, which is in the same family. The low carbon cladding has been fine too. Found it interesting and thought I'd share.