Finding a good knife for your food prep makes your work in the kitchen much easier and faster. So it can be very disappointing when your favorite knife rust. But why do knives rust?
Knives rust because their blades are made of metal alloys containing iron. When they come in contact with moisture or acidic substances, the iron in them rusts. The chances of rusting are higher in case of poor maintenance or improper storage. Knives will also rust faster in humid and coastal areas.
Let’s take a detailed look at this now.
What Causes Rust?
Rust is an ugly reddish-brown substance that grows on metallic surfaces.
It’s a chemical compound called iron oxide.
Rust forms when iron in a material reacts with oxygen in the air in the presence of moisture.
So if a metallic surface containing iron comes in contact with moist air, rust forms on its surface.
Now, kitchen knife blades usually contain iron.
However, this iron will not be in its pure form because it’s soft and highly prone to rusting.
Pure iron knives bend easily, rust quickly, and lose their sharp edge.
So pure iron isn’t the best material for a knife blade.
Instead of using pure iron, knife manufacturers prefer iron alloys.
Iron combines with other materials like chromium or carbon in these alloys to form stronger, corrosion-resistant blades.
Carbon steel and stainless steel are the most common alloys used for knife blades. Iron combines with carbon to form carbon steel, which is strong and durable.
Meanwhile, stainless steel is an alloy of iron and chromium.
Carbon steel and stainless steel have a higher resistance to corrosion than pure iron.
They are comparatively more inert to moisture.
Nonetheless, the iron in these alloys is not entirely impervious to water.
Placing them in a moist environment for a long time will make the iron oxidize and change into rust.
Stainless steel and carbon steel knives will also rust if you don’t dry them properly or store them away from moisture.
Recommended Further Reading:
- What Knives are Used by Professional Chefs?
- How Good are Cutco Knives?
- What Types of Pans Do Professional Chefs Use?
Carbon Steel vs. Stainless Steel Blades—What Rusts Faster?
Both carbon steel and stainless steel are used to make strong and durable knives.
However, these materials have slightly different properties due to their differences in chemical composition.
Carbon steel is more robust than stainless steel. It’s durable and has razor-sharp edges.
One of the best things about carbon steel knives is that they remain sharp for a very long time, making it easier to enjoy clean cuts for longer.
Stainless steel blades are not as sharp as carbon steel. They are softer than carbon steel and bend easily.
However, they are more durable and rust-proof.
The ability of stainless steel to resist rusting is because of the presence of chromium in them.
Chromium combines with oxygen to form an oxide layer on the surface.
This protective layer prevents iron from oxidizing. It slows down corrosion.
Since carbon steel lacks this protective oxide layer, it rusts faster.
So carbon steel knives need more care and maintenance.
They will stain and rust if you don’t dry them thoroughly and store them in a dry spot.
Now, this doesn’t mean that stainless steel knives are absolutely rust-proof.
They are more corrosion-resistant than carbon steel and pure iron.
However, they will also rust if you don’t maintain them properly.
Nevertheless, we recommend stainless steel knives over carbon steel knives if you live in a humid or corrosive environment, like near the sea.
Why Do Stainless Steel Knives Rust?
Stainless steel is hardy and highly rust-proof. However, stainless steel knives rust under certain circumstances.
The ability of a stainless steel knife to resist corrosion depends on the proportion of metals used in the alloy.
We already saw that stainless steel has chromium.
When exposed to air, chromium forms a natural oxide layer that prevents further oxidization of the blade.
The more chromium that a blade has, the better it can withstand rusting.
However, it’s still prone to rust when exposed to external factors like moisture, acid, and salt.
This means is that if the concentration of salt and water in the atmosphere is high, your stainless steel knife will rust faster.
Additionally, if you use the knife to cut acidic or salty products, it rusts easily.
You can prevent rusting of the blade to a great extent by taking good care of the knife.
Dry it well after washing and store it in a dry spot.
You can delay the onset of corrosion and use your knife for longer by taking proper precautions.
Why Do Japanese Knives Rust?
Traditional Japanese knives are made of Hagane, a form of carbon steel.
This material produces a sharp-edged blade that delivers clean cuts.
Some Japanese knives also use stainless steel.
Now, Hagane contains iron but no chromium. So it can rust.
Any contact with moisture and oxygen will cause the iron to turn into iron oxide or rust.
Leaving Japanese knives wet or soaking them in water for cleaning will hasten the rusting process.
Rust formation on the blade will affect its sharpness and its life.
Related Further Reading:
- Can Ceramic Bowls Go In The Oven, Microwave, or Broiler?
- Can Pots Be Used in an Oven?
- Are Dutch Ovens Made Of Cast Iron? [6 Materials They Are Made Of]
- Shun Knives: Where Are They Made and Their Unique Characteristics
Why Do Knives Rust In The Dishwasher?
The dishwasher is a valuable kitchen appliance that makes cleaning up easy.
However, all types of cookware and cutlery can’t go in a dishwasher.
Unfortunately, knives belong to this category.
Knives can develop rust spots and stains when you continuously wash them in the dishwasher.
This is because the cleaning process in a dishwasher is different from handwashing.
Multiple factors like prolonged exposure to heat and water, harsh detergent usage, and using salt for cleaning will contribute to the problem.
The moist environment of a dishwasher is not suitable for carbon steel and stainless steel knives because it increases the chances of rusting.
The heat used for cleaning can further accelerate the process.
Most dishwashing agents have strong salts and chemicals like chlorine. They increase the chances of rusting.
The chemicals and heat will also cause blades to lose their sharpness, and the metal can lose its natural luster.
Finally, if you let your knives drip dry after dishwashing, they have a higher chance of rusting.
Promptly remove the knives from the dishwasher and wipe them dry to prevent them from rusting.
Even if a manufacturer mentions that a knife is dishwasher-safe, we recommend handwashing to prevent rusting and to keep them in good condition for longer.
Can Global Knives Rust?
Global knives use molybdenum in their blades.
This mineral protects the blade against rusting or corrosion. So Global knives don’t rust easily.
Nonetheless, these knives will still rust if you don’t pay attention to cleaning and maintenance.
Rough cleaning with abrasive materials and strong detergents can damage the natural luster of these knives.
If you rub the surface with abrasive scourers and sponges, you will nick the stainless steel surface and expose the underlying iron.
When this happens, the knife will most likely rust.
Leaving the knife wet or exposed to moisture will also make it rust faster.
Can You Use Rusty Knives?
It can be disappointing when rust spots and stains appear on your precious knives.
When this happens, you may like to know if it’s safe to continue using them.
Well, the good news is that you can still use the knife if it’s not fully rusty.
However, you must get rid of the rust first.
Using the knife without removing the rust can introduce dangerous chemicals into the food and compromise food safety.
There are different ways to eliminate rust.
You can use natural rust cleaners like lemon juice, white vinegar, citric acid, and baking soda.
Depending on the extent of rust formation, you may have to use these products multiple times to eliminate the rust stains completely.
If you want a quicker solution for your rust problem, you can use chemical rust removers.
They are available in most local hardware stores and produce faster results than natural ingredients.
However, you must be very careful when handling them.
Follow suitable precautions to avoid harming your skin.
When rust appears on the blade, it will lose its sharpness.
So you may have to polish the blade to restore it to its original condition.
Interesting Further Reading:
- 8 Main Differences Between Fillet and Boning Knives
- Can Non-Stick Pans Be Used in the Oven?
- Are Dutch Ovens Non-Stick? [Cast Iron, Enameled, Le Creuset, Etc.]
- Can a Glass Bowl be Used for Double Boiler?
What Types Of Knives Don’t Rust At All?
Ceramic knives don’t rust. Although they are not all-purpose knives like carbon steel and stainless steel knives, they are your best bet when you need rust-free knives.
Ceramic knives don’t have metallic blades. So there’s no iron in them to rust.
Despite the absence of metal, these knives are sharp and affordable.
You will not have to worry about sharpening them frequently.
However, these knives are more prone to chipping and scratching than stainless steel and carbon knives.
Apart from ceramic knives, titanium and aluminum-coated knives are also more corrosion-resistant than pure carbon steel and stainless steel knives.