Yes - carbon steels such as Aogami (Blue) and Shirogami (White) react with food, moisture, and acids. Left wet they can spot or rust, and with normal use they develop a grey-blue patina. That patina is expected and is part of owning a carbon-steel knife; it is not damage.

Care is simple once it becomes habit: hand-wash in warm water, never leave the knife soaking or sitting in a wet sink, and dry it thoroughly the moment you finish. Avoid the dishwasher entirely, and wipe the blade between tasks when you are cutting acidic foods like citrus, tomato, or onion.

If the knife will sit unused for a while, wipe a very thin film of food-safe camellia oil (or a neutral mineral oil) onto the blade before storing it. A light surface rust spot lifts easily with a rust eraser or a little Bar Keepers Friend; sustained neglect is the only thing to really avoid.

Carbon steel rewards this small amount of attention with a keener edge and easier sharpening than most stainless. If you would rather not think about maintenance at all, ask us about stainless or stainless-clad options instead.

Blue 2 (Aogami #2) and White 2 (Shirogami #2) are both Hitachi high-carbon steels, but Blue 2 adds chromium and tungsten to White 2’s base, giving it noticeably better edge retention while keeping similar sharpness. The trade-off is that Blue 2 is slightly more abrasion-resistant during sharpening, so it takes a little more time to refine an edge, whereas White 2 is easier to sharpen and can take a finer, more aggressive edge but dulls faster in use.