Carbon steel is reactive by nature and will develop a patina over time as it encounters food, moisture, and air. This is not a flaw, it's the steel maturing, and a well-developed patina actually helps protect the blade. Wipe the blade clean between ingredients while cooking, wash by hand, and dry immediately after use. A light application of food-grade oil or wax before storage will keep it in excellent condition between sessions. With a little attention, this knife will only get better with age.