What is rust?
Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction if iron and oxygen in the presence of water or air moisture. Rust is typically associated with the corrosion of refined iron or steels with high percentages of iron.
Why do blades rust?
Remember that knife steel is primarily constructed with iron. While it is nearly impossible to eliminate the possibility of rust forming on your knife blade, there are certain measures that you can take to lower the possibility of it happening. Those measures include consistent cleaning and preventative maintenance.
After using your knife, do not just put it away and forget about it, leaving grime and moisture in contact on the blade. The best way to keep your knife from rusting is a good old-fashioned cleaning. It might be a little time consuming, but it is worth it. Additionally, a simple wipe down with vegetable oil is helpful for culinary knives, and a petroleum-based lubrication for utility knives, for example WD-40.
How to store knives
Rusting on your blade is inevitable. We discussed proper daily maintenance to prevent rust from forming, however, if it is not stored properly while not in use, most of that work will have been a waste of time. If you store your knife in a place that promotes rust, it will. When you are not using your knife the best place to store it is in a clean and dry area. To prevent potential scratching of the blade, I like to store it lightly wrapped it in a clean and dry terry cloth kitchen towel.