High-Carbon Steel - Carbon Steel has been used in the making of blades for many years. Carbon steel blades are tough, can be very sharp, retain their sharp edge fairly well, and sharpen with little effort. They have a tendency to be brittle and can break under stress. Carbon steel blades discolor when they come in contact with foods that are high in acid, such as tomatoes and citrus fruit. The discoloration does not affect the quality of the knife. With proper care, discoloration and rusting of the blade can be avoided and it can be treated if it does occur. Wash and dry thoroughly after use. If the blade rusts, scour to remove rust and continue to use. A light polishing with fine grit steel wool or sandpaper can also be used to remove the stains and rust from the blade.