Carbon steel isn't stainless. Leave it wet and it can rust, and with use it darkens to gray, blue and brown. That darkening is called patina, and it's normal.
The care comes down to three habits: wash the knife by hand, dry it right away, and hone it now and then.
We sell STEELPORT's carbon steel knives, so read this knowing that. We haven't tested any knife ourselves. What follows comes from makers' and knife shops' own care pages and the published makeup of the steel, linked at the end.
Why does it matter what your knife is made of?
In short. The steel decides the upkeep. Carbon steel wants a towel within a minute or two, and stainless forgives a wet counter.
You slice a lemon, set the knife down and go answer the door. When you come back there's a dark print on the blade where the juice sat.
That print is patina, and it does no harm. Orange specks would be rust, and those you'd scrub off. On a stainless knife, most likely nothing would have happened at all.
So the choice is about habits as much as sharpness. If the towel is already in your hand, carbon steel is easy. If knives wait by the sink until morning, it will show.
What is carbon steel?
In short. Steel with very little chromium in it. Stainless steels carry at least 10.5% chromium, and the 52100 steel in STEELPORT's knives carries about 1.5%.
Chromium is what makes stainless steel resist rust. The stainless industry's own association sets the floor at 10.5%.
STEELPORT forges its knives from 52100, which it calls a ball-bearing grade carbon steel. A published datasheet puts 52100 at about 1% carbon and 1.3 to 1.6% chromium, and it has been used in bearings since the early 1900s.
Knife shops often draw the line higher. Bernal Cutlery, a knife shop, calls anything under 13% chromium a carbon steel, and adds that every stainless can rust under the right conditions.
STEELPORT says it hardens the edge to 65 HRC, a hardness scale for steel, and leaves the spine softer at 30 HRC.
Why do cooks choose carbon steel?
In short. For the edge. Makers and knife shops say it gets very sharp and comes back quickly on a stone, and the price is the towel habit.
STEELPORT says its 52100 takes a sharper edge than most stainless steel and holds it longer. Chef Knives To Go, a knife shop, says carbon steel sharpens back up faster than almost anything else.
Those are sellers' statements, and edge claims are hard to check at home. One set of published cutting tests, summarized by the metallurgy site Knife Steel Nerds, found 52100 held an edge longer than a plainer carbon steel and less long than a stainless called AEB-L.
So the word carbon doesn't settle it. Which steel it is and how the maker hardens it matter as much.
What is patina, and is it rust?
In short. Patina is a thin, dark layer of oxidation that forms with use. Rust is orange or red, feels rough, and eats into the steel.
STEELPORT's FAQ says carbon steel changes hue over time from contact with hands, food and air. Its words for that: "That's normal (not rust)." It adds that patina doesn't affect how the knife cuts.
| Patina | Rust | |
|---|---|---|
| Color | Gray, blue or brown, sometimes a faint rainbow | Orange or dark red spots |
| Feel | Smooth, like the rest of the blade | Rough or powdery |
| What it is | A stable layer of oxidation on the surface | Active corrosion that works into the steel |
| What to do | Nothing. Keep cooking | Scrub it off soon, before it pits |
Acid speeds patina up. STEELPORT notes that citrus changes a blade's color far faster than vegetables do, which is why the lemon leaves a print and the carrot doesn't.
Patina also helps a little. STEELPORT, Bernal Cutlery and Opinel each describe it as some protection against rust. None of them says it replaces drying the knife.
There's no coating here to peel or wear through. The color is the steel's own surface, changed by what it has touched.
One plain consequence: the knife won't keep looking like its product photo. If you want a blade that stays bright, that's a stainless knife.
What is a forced patina?
In short. A patina the maker puts on before the knife ships. STEELPORT does it by steeping each polished blade in hot coffee.
That's meant literally. STEELPORT brews coffee strong, close to espresso, keeps it hot, and steeps each blade for less than an hour before rinsing and drying it.
The maker gives two reasons. The dark finish gives the steel a first layer of protection, and it shows the grain and the hardening line so each blade can be inspected.
STEELPORT says knife makers more often use etching chemicals such as ferric chloride for this. It tried vinegar, mustard, lemon juice and wine before settling on coffee.
A forced patina is a head start. The blade keeps changing as you cook with it, so a new knife and a two-year-old one won't match.
How do you care for a carbon steel knife day to day?
In short. STEELPORT's own line covers it: "Hand wash, dry right away, and hone regularly."
- Wash it by hand. Soap is fine. STEELPORT says never to put the knife in a dishwasher or leave it in the sink.
- Dry it right away. On a long prep, wipe the blade as you go too. Bernal Cutlery notes that acidic and salty foods react with the steel faster.
- Hone it. STEELPORT uses a ceramic rod at 17 degrees, three to five strokes a side. Honing straightens the edge between sharpenings.
- Oil it before a long rest. STEELPORT says to oil the blade regularly with a neutral oil such as camellia, and especially before long storage.
- Store it dry, with the edge covered. A block, a sheath or a wood-faced magnet all work. Loose in a drawer chips the edge.
- Cut on wood, hard rubber or soft plastic. Plates and stone counters dull any knife.
Most days that's a dish towel and ten seconds.
The board matters to the edge as well. Our guide to cutting board finishes covers what wood boards are oiled with.
What do you do about a rust spot?
In short. Scrub it off gently, and soon. Light rust caught early takes a few minutes.
STEELPORT describes rust as dark red or orange spots and says to remove it before pitting can begin.
Start mild. Chef Knives To Go suggests a paste of baking soda and water, worked in with a soft cloth or sponge, then a rinse and a full dry. Opinel lists baking soda with vinegar, or a powdered scrubbing compound, rubbed along the length of the blade.
Use the finest abrasive that works. Bernal Cutlery's reason is practical: coarse scratches give water a place to sit, and that invites more rust.
The scrubbed patch may look brighter than the steel around it. Patina fills back in with use.
Rust left for weeks is different. It can pit the steel, and Chef Knives To Go says deeper rust may leave cosmetic marks even after it's gone.
Who should buy stainless instead?
In short. Anyone whose knives wait in the sink or ride in the dishwasher, and anyone who wants a blade that stays bright.
Carbon steel is a good fit if you:
- already dry your knife before you put it down
- like tools that show their use
- hone or sharpen your own knives, or want to learn
Buy stainless if you:
- leave knives by the sink until morning
- live with someone who puts everything in the dishwasher
- want the blade to look the same in five years
- cut a lot of citrus and tomatoes and don't want to wipe between jobs
Opinel sells both kinds and says as much: for easy maintenance, it recommends its stainless blades.
Stainless still isn't a free pass. Bernal Cutlery says no knife comes through a dishwasher unharmed, only more slowly.
If carbon steel suits you, the STEELPORT knives we carry are in our knives collection.
Common questions
Is patina on a carbon steel knife normal?
Yes. STEELPORT says carbon steel changes color over time from contact with hands, food and air, that this is normal, and that it doesn't affect performance.
Will a carbon steel knife rust?
It can, if it's left wet. STEELPORT says plainly that its carbon steel knives are not stain or rust resistant. Washing by hand and drying right away is what prevents it.
How do you tell patina from rust?
By color and feel. Patina is gray, blue or brown and smooth. Rust is orange or dark red and rough, and it should be scrubbed off.
Why did my knife change color after cutting a lemon or an onion?
Acid speeds up patina. STEELPORT notes that citrus changes a carbon steel blade's color much faster than vegetables do.
Can a carbon steel knife go in the dishwasher?
No. STEELPORT says never to put its knives in a dishwasher or leave them in the sink.
How do you remove rust from a carbon steel knife?
Rub the spot with a paste of baking soda and water on a soft cloth, then rinse and dry the blade fully. Knife shops say to use the finest abrasive that works.
Do you need to oil a carbon steel knife?
STEELPORT says to oil the blade regularly, and especially before long storage. It uses a neutral oil made from camellia seed.
What is 52100 steel?
A carbon steel with about 1% carbon and 1.5% chromium, first made for ball bearings. STEELPORT forges its knives from it and hardens the edge to 65 HRC.
Is carbon steel better than stainless steel for knives?
It depends on the steel and on you. Makers say carbon steel takes a very sharp edge and resharpens quickly, and it needs drying after every use. Stainless asks less.
Read next: Carbon steel vs stainless steel knives: which should you buy?, Cutting board finishes: mineral oil, beeswax and coconut oil, What 18/8, 18/10, 304, 316, and 430 actually mean, for the chromium numbers on the stainless side, and Is the rainbow on my pan a coating?, where a different steel changes color for a similar reason.
Sources
A maker or shop page tells you what that business states. It isn't independent proof.
- STEELPORT Knife Co., FAQ (52100 steel, 65 HRC, care line, patina, honing rod). steelportknife.com. VERIFIED, maker statement.
- STEELPORT Knife Co., Care and Use (dishwasher and sink, blade oil, rust spots, storage, cutting surfaces). steelportknife.com. VERIFIED, maker statement.
- STEELPORT Knife Co., 8 inch Chef Knife (not stain or rust resistant, coffee patina, 30 HRC spine). steelportknife.com. VERIFIED, maker statement.
- STEELPORT Knife Co., STEELPORT Coffee Patina for Protection and Presentation (what patina is, acid, the coffee method). steelportknife.com. VERIFIED, maker statement.
- worldstainless, Introduction to Stainless Steels (minimum 10.5% chromium). worldstainless.org. VERIFIED, industry association.
- AZoM, AISI 52100 Alloy Steel datasheet (carbon 0.98 to 1.10%, chromium 1.30 to 1.60%, used in bearings). azom.com. REPORTED, materials reference site.
- Knife Steel Nerds, History and Properties of 52100 Steel (bearing steel in use since at least 1905, published edge tests against other steels). knifesteelnerds.com. REPORTED, secondary source citing published tests.
- Bernal Cutlery, Knife Care (carbon and stainless by chromium content, patina, rust removal, dishwashers). bernalcutlery.com. VERIFIED, knife shop statement.
- Opinel USA, Care and Maintenance (carbon steel blades, patina, restoring a rusted blade, stainless for easy maintenance). opinel-usa.com. VERIFIED, maker statement.
- Chef Knives To Go, Carbon Steel Knife Care Guide (patina and rust colors, rust removal, sharpening). chefknivestogo.com. VERIFIED, knife shop statement.
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