When you are done using your carbon steel kitchen knife, hand wash it with soap and water and thoroughly dry it. If you’d like, you can wipe the blade with just a bit of olive oil or other cooking oil before you put it away, but you don’t have to. This simple bit of routine care should be all you need.
Since carbon steel has no stain resisting properties of its own, with regular use in preparing food, irregular oxides will form on the surface of your blade. These are not harmful or unsafe and the longer you use the knife, the development of oxides will eventually slow until a rich patina develops. This is normal and to be expected with a carbon steel blade, so try not to panic the first time you cut a lime and watched your shiny new blade turn a splotchy grey!
Don’t leave the knife soaking in the sink and NEVER PUT THIS KNIFE IN THE DISHWASHER! A dishwasher has a sand blasting effect on the edges of fine knives.
If acid or water sits on the surface of the blade, deep pitting or red rust may appear. Scrub those spots with a green Scotchbrite scrubber or some 600 grit sandpaper. If the blade is already patinated from use it will create a shiny spot. Use as normal and the patina will reestablish itself.
Sharpening should be done on a fine stone or steel. Do not use any sort of “pull through” sharpener.