How to care for a carbon steel knife: patina, rust, oiling and sharpening
Updated · 8 min read
Carbon steel knives have a loyal following. Many cooks and makers like how keen an edge they take and how easily they can be brought back on a stone. The trade-off is that they rust if they are left wet, and they change colour as you use them. Stainless knives are more forgiving, but they behave differently.
None of the care is difficult. It comes down to three habits: wash and dry the knife straight after use, keep a thin film of oil on it when it is stored, and cut on a board that does not damage the edge. The rest is knowing which marks are normal and which need attention.
If your knife came from a smith or a small workshop, their care card comes first. What follows draws on manufacturers' and specialist retailers' published guidance, for when you want to understand the reasons.
Key takeaways
- Carbon steel rusts if it is left wet. Opinel states plainly that carbon blades will rust if not cared for properly.
- A grey, blue or dark patina is normal and, according to Opinel and Chef's Armoury, helps protect against rust.
- Wash by hand, dry straight away and never use the dishwasher.
- Store the blade clean, dry and lightly oiled with a food-safe oil.
- Cut on wood or soft plastic. Chef's Armoury warns against glass, ceramic and stone surfaces.
- Hone regularly and sharpen on whetstones when honing stops working. Shun suggests once a year is probably enough for most home cooks.
Carbon steel and stainless steel
All knife steel is iron with carbon. Stainless steel adds chromium. Euro Inox, the European stainless steel development association, explains that stainless steels must contain at least 10.5% chromium by weight, as defined in the European standard EN 10088-1. The chromium forms a thin, self-repairing oxide layer on the surface, which is what resists corrosion.
Carbon steel knife blades do not have enough chromium for that protective layer. That is why they react with water, acids and salt, and why they need more attention. Opinel, which makes both types, describes its stainless 12C27 steel as containing 14.5% chromium, and its carbon XC90 steel as one that will patina over time and rust if neglected.
Many hand-forged knives combine both. A carbon steel core can be clad in softer iron or stainless steel. Retailers of these knives point out that cladding helps, but the exposed carbon edge still rusts if it is left wet. Ask your maker what your blade is made of.
Patina and rust
These are the two marks people most often confuse.
| Patina | Rust | |
|---|---|---|
| Colour | Grey, blue, purple or near black, often uneven | Orange or red-brown |
| Texture | Smooth, part of the surface | Raised, powdery or pitted |
| Cause | Acids and moisture in food reacting with the steel | Water or damp left on the blade |
| What to do | Nothing. It is normal | Remove straight away |
Opinel says its carbon blades are expected to patina and that the patina helps with rust resistance. Chef's Armoury lists foods that tend to create patina quickly, such as onion, garlic, chives, artichoke and cabbage. If you prefer a brighter blade, rinse the knife as soon as you have cut these foods.
Patina is not a guarantee. A patinated blade left wet in a sink will still rust.
Daily care
- Wash by hand. Opinel suggests a damp cloth with a touch of mild washing-up liquid only if needed.
- Dry straight away. Opinel says to dry carbon blades with a soft, dry cloth as soon as they are wet. Chef's Armoury suggests a paper towel and says not to store a knife unless it is fully dry.
- Never soak it. Leaving a knife in water is the fastest route to rust.
- No dishwasher. Opinel and Chef's Armoury both say this, and so does STEELPORT, a Portland knife maker that forges carbon steel blades, on its own care page: hand wash and hand dry, never the dishwasher, never left in the sink. Opinel's own wording is specific: its French site says pocket knives should not go in the dishwasher, and Opinel USA says wooden-handled knives, folding or kitchen, are not designed for it.
- Oil before storing. A thin coat of food-safe oil keeps humidity off the steel.
Which oil
Use a food-safe oil. Opinel names mineral oil and olive oil as food-safe options. Chef's Armoury recommends camellia oil for the exposed carbon steel after use. Some camellia oils sold for knives include other ingredients and are not meant for cooking, so read the label if the knife touches food. If your maker supplied an oil, use that.
Removing rust
Act early. Chef's Armoury advises removing rust immediately so it does not spread, using a rust cleaner for light marks and a rust eraser or very fine abrasive paper for heavier ones. Opinel says to grind or brush away any rust before you use the knife on food.
Abrasives scratch the finish as well as the rust. On a hand-forged blade with a decorative finish, or if there is pitting, ask the maker before you start.
Cutting boards and use
The edge on a thin carbon blade is hard and fine. Opinel recommends cutting on wood, bamboo, composite or food-grade plastic and avoiding glass, marble and ceramic. Chef's Armoury suggests an end-grain wooden board or soft plastic board and warns against cutting on hard surfaces such as worktops.
Retailers of hand-forged carbon knives also advise against cutting bone, frozen food and hard seeds, which can chip a hard edge. Use a heavier knife or a cleaver for those jobs.
Storage
Chef's Armoury suggests storing knives in their box, a wooden sheath (saya), on a magnetic rack or in a knife block. It warns against plastic and leather sheaths, which can trap moisture against the blade. In a drawer, a blade guard protects both the edge and your fingers.
Always store the knife dry and lightly oiled, especially if it will not be used for a while.
Honing and sharpening
Honing and sharpening are different jobs. Shun explains that the edge gradually rolls over with use, and a honing rod realigns it without removing metal. Sharpening removes metal to create a new edge.
- Honing. Shun says some cooks hone daily and some weekly, depending on use. Chef's Armoury recommends a fine ceramic rod for carbon Japanese knives rather than a coarse or diamond rod.
- Sharpening. Shun says to sharpen only when honing no longer works, and that once a year is probably more than enough for most home cooks. Chef's Armoury recommends Japanese waterstones and advises against pull-through sharpeners, hot grinders and belt sanders.
- Angle. The right angle depends on the knife. Opinel gives 15 to 20 degrees per side for its pocket knives, and Shun uses 16 degrees for its knives. Ask your maker what angle they ground.
Many makers offer sharpening as a service. If you are new to whetstones, a session with the maker or a professional sharpener is a good start.
Wooden handles
Water damages wooden handles as well as blades. Opinel says to keep handles as clean and dry as possible, and that long soaking can make them split or warp. Hand wash and dry the handle along with the blade. Some retailers of carbon knives suggest an occasional wipe of wood oil on the handle. Use whatever your maker recommends for the specific wood and finish.
Carrying knives: a brief note on the law
This guide is about care, but owners sometimes ask about carrying knives. It is not legal advice.
- UK. GOV.UK says it is illegal to carry most knives in public without a good reason. The exception is a folding pocket knife with a cutting edge of 3 inches or less that does not lock. Examples of good reasons include taking a knife to work, religious reasons and national costume. A court decides whether a reason is good enough. In England and Wales the offence is in section 139 of the Criminal Justice Act 1988, which exempts folding pocket knives with a cutting edge of up to 3 inches and lists use at work, religious reasons and national costume as defences. Northern Ireland has its own version of the section, and Scotland has separate legislation.
- Poland. Article 50a § 1 of the Code of Petty Offences (Kodeks wykroczeń) penalises having a knife, machete or similar dangerous object in a public place when the circumstances indicate intent to use it to commit a crime. The penalty is detention, restriction of liberty or a fine of at least 3,000 zł, and the object is forfeited.
Transport a new kitchen knife wrapped and out of sight, and check local rules when you travel.
Keep the care card
A hand-forged knife often comes with notes on the steel, the handle wood and the sharpening angle. Keep them with the knife or on your phone. If you ever need a repair or a regrind, the maker or a sharpener will want to know what the blade is made of. For how makers prepare these, see our guide to care cards for handmade objects.
This guide is general information, not legal advice. Laws change, and how they apply depends on the facts of each case. Before a decision about your own contract, product or business, check the current text with the relevant authority or ask a lawyer.
Sources
- XC90 carbon steel and 12C27 stainless steel, Opinel USA: patina and rust on carbon blades, mineral and olive oil, 14.5% chromium in 12C27, sharpening angle of 15 to 20 degrees for pocket knives
- How to take care of your folding knife, Opinel USA: washing, drying, food-grade oil, no dishwasher, cutting surfaces, keeping wooden handles dry
- Care and use, STEELPORT Knife Co.: a knife maker's own care page: hand wash and dry, no dishwasher or sink, oil before storage, patina is normal, remove rust before pitting, avoid loose drawer storage
- Cleaning your Opinel, Opinel and Opinel FAQ, Opinel USA: pocket knives never in the dishwasher; wooden-handled knives not designed for it; polymer handles only very occasionally
- Japanese knife care: 100% carbon steel knives, Chef's Armoury: drying, camellia oil, patina-forming foods, rust removal, storage, cutting boards, waterstones, ceramic rods, no pull-through sharpeners
- Sharpening and keeping them sharp, Shun catalogue: honing versus sharpening, rolled edge, honing frequency, once-a-year sharpening, 16-degree angle
- Pickling and passivating stainless steel, Euro Inox: minimum 10.5% chromium under EN 10088-1, self-repairing passive layer
- Blenheim Forge knives, Borough Kitchen: care for clad and carbon hand-forged knives, avoiding bones and frozen food, storage
- Robert Herder 1922 office knife, carbon, Old Faithful Shop: patina as harmless, do not leave in water, wood oil on handles
- Buying and carrying knives, GOV.UK: folding pocket knife exception, good reasons, court decides
- Criminal Justice Act 1988, section 139, legislation.gov.uk: offence of having a bladed article in a public place, 3-inch folding pocketknife exception, defences, extent
- Obwieszczenie Marszałka Sejmu w sprawie jednolitego tekstu ustawy – Kodeks wykroczeń, Dz.U. 2026 poz. 1372: article 50a text and penalties
Questions this guide gets asked
Is the dark colour on my carbon steel knife rust?
Probably not. Opinel says its carbon blades are expected to patina over time and that patina helps with rust resistance. Patina is a grey, blue or dark film that forms with use, especially after cutting acidic foods. Rust is orange-brown, raised or flaky, and should be removed before the knife touches food.
Can a carbon steel knife go in the dishwasher?
No. Opinel advises against dishwashers for its carbon folding knives and wooden handles, and Chef's Armoury says never to put carbon steel knives in one. Long contact with water and detergent encourages rust and can damage wooden handles.
What oil should I use on a carbon steel blade?
A food-safe oil. Opinel names mineral oil and olive oil as food-safe options, and Chef's Armoury recommends camellia oil. Apply a thin layer to a clean, dry blade, especially before storing the knife for a while. If your maker supplied or named an oil, use that.
How often should I sharpen my knife?
Less often than you might think, if you hone. Shun, a Japanese knife brand, says some cooks hone daily and some weekly, and that once-a-year sharpening is probably enough for most home cooks. Sharpen when honing no longer brings the edge back.
How do I remove rust from a carbon steel knife?
Light rust can be removed with a rust eraser or very fine abrasive, according to Chef's Armoury, which advises removing rust straight away so it does not spread. Opinel says to grind or brush away rust before using the knife on food. For deep pitting or a hand-forged blade you value, ask the maker.
Is it legal to carry a kitchen or pocket knife in the UK or Poland?
In the UK, GOV.UK says you can usually carry a folding pocket knife with a cutting edge of 3 inches or less that does not lock, and other knives only with a good reason. In Poland, article 50a of the Code of Petty Offences penalises having a knife in a public place when the circumstances suggest intent to commit a crime.