Carbon steel knives are a preferred tool for professional chefs and homecooks alike. The steel takes a more keen edge, and holds it for longer than most stainless variants. Carbon steel is, however, a more care-intensive material. Because carbon steel is often harder and ground thinner than commercial knives, they are more prone to chipping, or even shattering. In addition, the steel is reactive because it does not contain as much chromium, which is what makes commercial knives stainless. A carbon steel knife will rust if left dirty or wet for prolonged periods of time. Here are a few tips to keep your knives in top shape.
Keep a slightly damp towel by your cutting board, and wipe the blade clean when not in use. Wipe completely dry before storing.
Apply a food-safe oil to the handle and blade occasionally. This will protect the blade from rust, and rejuvenate the wood in the handle.
Hand wash your knives with soap and water. NEVER wash your knives in the dishwasher. Dish-washing detergent is corrosive to the steel, and will likely damage your knife irreparably.
Carbon steel knives develop a patina with use, this means that the knife will have a gray/blue-green tint to it where it has reacted with the food it has cut. A patina will help resist corrosion. Be mindful of the color of the steel, rust and corrosion appears red, orange, or brown.
If you do encounter rust, scrub the affected areas with the scrubbing side of a sponge or a Scotch-Brite Scouring Pad. Continue until the rust is gone and the area is smooth to the touch. Apply a food-safe oil and store.
Store knives in a safe place where the edge and tip are not being jostled by things around it. A drawer is not a safe place to store a knife, for your knife or for whoever reaches into the drawer to grab it. Knife blocks and wall magnets are great options for safely storing a knife.
Keep your knives sharp. A sharp knife is a safe knife, as less pressure is needed to cut things, reducing the chance of your knife slipping. Sharpen your knives on whetstones, not on grinding wheels. These stones are much more gentle, and produce a far superior edge. I recommend a 1000/6000 water stone for beginners. Avid homecooks and professional chefs should sharpen their knives regularly, every 1-3 months. Less-inclined users should have knives sharpened 2-3 times a year.
Gently hone your knives as to not unintentionally dull the blade. To properly hone your knife, take your honing rod in your non-dominant hand and anchor the tip down on a towel or cutting board. Looking down the spine of your knife, tilt the knife to have the edge meet the rod, at approximately 15 degrees. Using only the weight of the knife, hone the edge in one smooth, downwards motion from heel to tip. Each pass, switch the side that you're honing by either flipping the knife upside down, or by carefully reaching the knife around to the other side of the rod, and repeat. After 10 or so passes, you're done. Test your edge. If honing does not improve your edge, the knife needs to be sharpened.