However, as great is carbon steel, daily and regular use has the knife exposed to natural destructive force: rust.
No need to fret, as it’s not the end of the road for your favorite kitchen knife.
Following, we’ll show you how you can successfully clean and care for a carbon steel knife.
- 1 What is Carbon Steel Blade?
- 2 How to Clean Carbon Steel Knives?
- 3 Using Oils on the Knives
- 4 Patina on a Carbon Steel Block
- 5 Accelerate Patina Formation – Avoid Rust Forming
- 6 Rusting and Corrosion of High Carbon Steel Knives
- 7 How Fast Does Steel Rust?
- 8 If a Knife Rusts – Rust Removal
- 9 Conclusion
What is Carbon Steel Blade?
Carbon steel knives are made of iron and carbon and opposed to stainless-steel knives, are characterized by a high carbon content of around 2-2.5% or even 3.8%.
The high carbon concentration gives the blade strength and toughness, and they are more durable than stainless steel. It requires sharpening less often; the blades are sharper and stronger.
This kind of steel is also easy to recycle, making it environmentally friendly. Professional chefs often prefer carbon steel but it is a great choice for home cooking.
How to Clean Carbon Steel Knives?
After every usage, immediately wash the knife with your hands, and wipe it dry with a clean, soft cloth. This way, you will remove moisture from the surface and prevent corrosion.
Avoid keeping your knives in a knife block: they are not sanitary and dull the blades every time you take out or put them back.
Use a magnetic strip or rack instead. Besides, it will allow them to dry quickly, while moisture can be present for longer in the knife block.
Don’t put carbon steel knives in the dishwasher. The moisture and detergents can quickly blunt your blade and enable corrosion and rust formation.
Using Oils on the Knives
Using oil on carbon steel blades regularly means an extra step of protection. Oils do not allow water and oxygen to get in contact with the blade, preventing corrosion and rusting.
The best types of mineral oil are canola or corn oil. Many other types of food-grade mineral oil can resin over time and get sticky.
Additionally, you can use wax as well. Not only the blade, but the handle can be treated with oil or wax (wood handles). After washing the knife, wipe it dry, and apply oil or wax with a cloth.
When covered, remove excess oil by wiping it with another clean cloth. A light coating will be enough to prevent the knives but won’t get sticky.
Patina on a Carbon Steel Block
Carbon steel blade’s alloy content had to be under 10.5%, which makes them more sensitive to corrosion and rusting when exposed to moisture for extended periods time.
Together oxygen and moisture will lead to corrosion, and the blade starts to change color – a mixture of grey, blue, and black. Additionally, acids can accelerate patina formation, such as cutting a tomato, onion, lemon, and other acidy foods.
This dark layer is called patina, which makes the knife unique, and some find it aesthetically pleasing as well. Actually, patina formation is not a bad thing.
It protects the blade from further corrosion as an extra layer, and the well-known red rust will not appear and destroy your carbon steel knife.
Hence, as long as your knives have a dark patina layer, don’t worry. However, if your knife starts to become red or orange, that is not a good sign because rusting started.
Accelerate Patina Formation – Avoid Rust Forming
As patina protects the knife from rusting as an extra layer, its appearance is desirable. Patina formation can be accelerated by using mild acids, such as acids found in coffee. Use the cheapest, worst quality of coffee you can find because they have high acid content.
Brew the worst and strongest coffee of your life, pour it in a high vessel, and dip your knife in it. Make sure that the coffee cooled down and the handle is not submerged. Additionally, you can put a piece of sponge on the bottom to protect the sharp tip of the blade.
Leave the knife in the coffee for at least 6-8 hours, but preferably overnight. After the procedure, take the knife out, clean it off, and dry it thoroughly. A nice patina layer will be seen on the blade after the treatment.
Rusting and Corrosion of High Carbon Steel Knives
Anything with high iron concentration can rust over time. In stainless steel knives, high chromium content prevents rust formation for a longer time. Iron, when exposed to oxygen and moisture, will rust and in case of a high carbon steel knife, it happens quicker. Rusting is a chemical reaction called corrosion.
The rust formation only occurs on the outside of the blade’s surface because the material must be directly exposed to oxygen and water.
As the blade corrodes and rust appears, the porous rust layer – permeable to water and air – will allow further corrosion in the deeper layers. This is why it is crucial to maintain your knives, and if rust occurs, remove them properly. You can read more about how to take care of your carbon steel knives in the article.
How Fast Does Steel Rust?
Shortly, corrosion will occur instantly after every usage of a high carbon blade. The chemical reaction is not fully preventable because it starts quickly when the blade is wet, and oxygen is present in the air.
Although the chemical reaction occurs immediately, you won’t notice it for a while. Rust formation takes time, and if you take care of your knives properly, it can be 4-5 years. In comparison, in the right conditions – being exposed to moisture and oxygen for an extended period of time – rust formation can be seen in 1-2 weeks.
If a Knife Rusts – Rust Removal
Eventually, rust formation can be seen – but this is not the end of your knife’s life. Removing rust is not difficult: there are multiple ways you can keep knives from rusting at home.
Generally, anything that is acidic enough will be able to remove rust, as the oxidized and intact iron will separate. Something abrasive will also be needed to grind the rust from the blade. The vinegar , baking soda , potato , and lemon juice method can all help you clean your knife and remove rust spots.
Removing rust by using vinegar will guarantee your success but also a bit more dangerous than the other methods because vinegar is more acidic.
If you are not careful enough, it can hurt the blade and do more harm than good. It is better to use on less expensive and/or very rusty blades. However, on expensive, high-quality knives and minor rust, the baking soda and potato methods are desirable.
First, clean your knife with water and wipe it dry with a clean cloth. Next, soak a paper towel in white vinegar (only white – don’t use other types) and wrap your blade for a maximum of five minutes.
If the rusting is not severe, even one minute will do the job. Remove the paper towel and use a sponge to scrub the blade. Be careful, and don’t scrub too hard, not to hurt the deeper layers or the patina.
If the process does not remove all the rust, try the baking soda or vinegar method to get rid of the rest. Once done, treat the blade with food-grade mineral oil, and sharpen it, as the process might dull the edge.
Baking Soda Method
For this method, you will need baking soda, a scrubbing pad, a dry cloth, and mineral oil. Clean the knife and dry it with a soft cloth. If possible, don’t use water for cleaning; prefer a non-abrasive cleaning solution. However, if you must use water, wait until the blade is completely dry.
Next, mix baking soda with water to get a light paste – it shouldn’t be a liquid but use enough water to get a smooth consistency. Apply baking soda on the surface rust, laying it flat, and leave it on for 5 to 30 minutes, depending on the severity of rust.
After that, scrub the blade with a scrubbing pad or steel wool until the rust is removed. You can apply more paste as needed until the rusty layer is removed. Repeat the process on the other side.
A safer version of the baking soda method includes using a wine cork or aluminum foil because it will scratch the knife. It takes longer to remove the rust but worth the effort if the knife is very expensive or important to you.
When both sides are clean of rust, clean the blade, remove the baking soda paste, and apply a thin layer of mineral oil for extra protection. If needed, sharpen the blade after the process using a sharpening stone.
The potato method is the least effective but can be enough if only minor rusting occurred. Clean the knife, dry it, and stick the blade into the potato (just cover the rust spots), and leave it in for an hour.
After an hour, rub it gently with a fine sponge, use a dry cloth to clean after the process, and treat the blade with mineral oil.
Lemon Juice Method
Mix an equal amount of warm water and lemon juice and soak the blade in the mixture for no more than 10 minutes. In case of severe rusting, use a scrub or steel wool to remove it after the treatment. To prevent scratching, use a cloth, aluminum, or wine cork instead.
Alternatively, cut a lemon half, rub the blade with the pure lemon juice, and then use a scouring pad to remove the rust. Instead of using lemon, some citric acid powder will do the job as well. After the treatment, wash and dry the blade, treat with food-grade mineral oil, and sharpen if needed.
Taking care of your knives will help you use them for years without rust formation. But if it happens, you can remove the rust in many ways at home without hurting the blade.
Carefully follow the steps in order not to scratch the high carbon blade because that can accelerate corrosion.