Dark stains on stainless steel knife blades (common even on high-quality products like those from Domus & Design) are usually caused by oxidation or deposits of limescale and mineral salts contained in water or food residue. Here’s how to safely remove them without scratching the steel: 1. The natural remedy: Lemon Juice or Vinegar. The acidity of lemon or white vinegar is perfect for dissolving light oxidation stains. How to: Dampen a soft cloth with lemon juice or vinegar and gently rub the blade. Let it sit for a couple of minutes, rinse, and—essentially—dry immediately with a microfiber cloth. 2. Baking Soda Paste (for Stubborn Stains) If the stains are darker or stubborn, baking soda acts as an ultra-gentle abrasive. How to: Create a thick paste by mixing baking soda and a little water. Apply it to the stain and scrub with a soft sponge (never the abrasive part!), following the direction of the steel’s satin finish. Rinse and dry thoroughly. 3. Specific Polish for Steel If natural remedies aren’t enough, there are specific metal cleaning creams (such as Sidol or similar for steel). Caution: Use very little and be sure to wash the knife thoroughly with dish soap after use, as they are not food products. 4. Why do they appear and how do they prevent them? Knife blades are made of a different steel (often 420 or 440) than forks and spoons (usually 18/10) to allow for sharpening. This makes them slightly more sensitive to external agents. Avoid soaking: Never leave dirty or wet knives in the sink. Dishwasher: If you wash them in the dishwasher, remove them as soon as the cycle is finished. The hot, moist steam “cooks” the mineral salts on the blade, creating dark stains. Contact with other metals: Do not wash knives in contact with silver or aluminum objects (galvanic effect that causes stains).