What’s that stain on your blade? Is it dirt? Is it rust? Is it a sign that your knife is damaged? Chances are, it’s none of the above. Chances are, what you have is a patina.
Patinas are thin layers that form on steel due to corrosion. It’s something that every chef and knife enthusiast should know about.
It’s so important to learn about patinas because they appear in almost every knife. If you’re uninformed, you may panic when you see one. There is no need because unlike other types of corrosion, patinas are not a bad thing.
So what are patinas? How do they appear on your blade? How do you remove them? Let’s answer all of these questions and more right now!
What is Patina?
One thing I’ve learned as a knife enthusiast is that carbon steel knives need maintenance. And by maintenance, I mean a lot of maintenance. Unlike stainless steel knives, it’s very easy for these steels to corrode.
That’s why after every use, I make sure to clean and dry them. Any moisture left on their surface will result in rust popping up. Despite this proper care, you may still find some stains on your blade.
These grey discolored stains are patinas. Like rust, it forms from a chemical reaction in the steel. When the air oxidizes the iron of your steel, it forms the compound Fe3O4, also known as magnetite. This gives blades their patinas.
Fe3O4 is the most basic type of patina. In reality, there are several other elements that get added to the mix as well. These include other carbonates, sulfates, and oxides.
That’s why every patina is different. It is near impossible to get the same patinas on two different knives. As your knife ages, it will develop its own unique patina design.
It’s very difficult to prevent patinas from forming. Stopping rust is one thing, avoiding patinas is another. That’s why almost every carbon steel knife will get a patina eventually.
The good news is that a lot of people like patinas. They like the look it gives their knives, as well as its protective properties (more on this later). So patinas forming is not necessarily a bad thing.
Personally, I don’t mind patinas. It’s all a matter of preference. You may hate the “dirty” looks it will give your knife, or you may love the pattern it forms on your blade.
If you don’t like patinas, it’s good to know how they form. This way, you can prolong the shiny surface of your blade. Let’s find out right now in…
How Do Patinas Form?
So patinas form when the iron in your blade oxidizes… what does this mean? How does oxygen combine with the iron in your carbon steel?
The process is a lot simpler than it sounds. If you leave your knife out in the open, it will oxidize. So is that all there is to patinas?
No. If you’re someone who wants a patina to form, neglect is not the right way to do this. You should never neglect to take care of your knives.
If you use your knives and leave them out in the open without any cleaning, you’ll get rust. And as we’ll see later on, rust is far worse than patinas.
While rust isn’t too difficult to prevent, patinas form even when you take care of your knife. The moment you touch the steel, you are already affecting the chemical compounds in it. And whenever you use your knife, this affects the steel in small ways.
If you use your knife, patinas will form over time. Acidic substances, such as food and fruits, affect steel the most. Cutting these types of things will get the patina to form faster.
On the other hand, if you don’t want a patina on your knife, there are some ways you can prevent it. Taking very good care of your knives will certainly help. Always wash and dry your knives after every use.
But won’t patinas form regardless? Yes, they will, but a lot slower. But there’s no need to worry. There are some ways to remove patinas which we’ll look at in a bit.
That’s why we should take care of our knives. You absolutely do not want rust on your knives. But why is rust so much worse than patinas anyway? Let’s take a look at…
Rust vs Patinas
Both rust and patinas are signs of corrosion on the blade. So why do we avoid rust at all costs, but tolerate, sometimes even welcome, patinas?
To start, let’s take a look at rust first. Like patinas, basic rust is a combination of iron and oxygen. Its composition is less than patinas at Fe2 O3.
That’s how close these two compounds are. Rust is only one iron and oxygen molecule away from patinas. Yet this small change makes all the difference.
We all know what rust does. That orange compound can eat at steels very quickly, and destroy it forever. You know you’ve mistreated your knife when you see rust spots on it.
Patinas, on the other hand, are black or grey. They don’t eat at steel as rust does, so leaving them on is okay. And unlike rust, you don’t have to mistreat a knife to get patinas on it.
Another difference is how they come about. The easiest way to get your knife rusted is by wetting it. If you leave your knife moist, expect to see rust on it the next day.
Whereas patinas are formed more by acid. Acid affects steel in such a way that brings this out. But it isn’t only when you cut fruits and food. When you hold a blade, the sweat in your hands also affects the steel and creates patinas.
Rust looks terrible. Not only does the orange of rust mean your knife is degrading, but it also looks awful. Compare this with the black and greys of patinas, and you’ll see a huge difference.
Patinas can look very good. There are some people today who prefer smooth and shiny steel. But there are others who want a more rugged look. That’s exactly what a good patina will give you.
Finally, both rust and patinas can form in any knife. They’re more common in carbon steel knives because of the lack of chromium. But they can also affect stainless steel knives as well.
Now that you know the difference between patinas and rust, you may still be wondering, “Why would anyone want patinas at all?”
Yes, they’re not as bad as rust, but what can they do?
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What Patinas Do
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Hearing that a patina is a sign of corrosion, you may think its crazy for some people to want it. I certainly thought this the first time I heard of this. But at the same time, I got very curious. Why would anyone want a patina?
It turns out, some people love the looks of patinas. There’s something about the ruggedness of patinas that makes it charming. With a patina, your knife will look like the real deal.
Again, it’s all preference. For some, the patterns created by patinas adds character to their blade. For others, it just looks dirty.
But that’s not the only thing that patinas do. No, it’s not all decoration. There is also something else that makes patinas worth having.
That is its rust preventive properties!
But wait! Aren’t patinas and rust related to one another? Why will a patina prevent rust from forming?
It’s simple, rust won’t form because there is already something else on your steel. The trick is to get your steel to form Fe3O4 instead of Fe2O3. Rust won’t settle on your blade because it won’t have any space.
This is another reason why some people force patinas into their blades. They want it not only for the looks but also to protect their blade. Again, the last thing you want is a rusted blade.
Sounds good, doesn’t it? I’ve tried this on several blades, and it does indeed prevent rust.
However, this doesn’t mean you will never get rust when you have a patina. You still have to take good care of your knife. A patina is simply another protective layer, not a complete stop to rust.
How to Form Patinas
Patinas will form naturally over time. The more you use your blade, the sooner you are likely to see one. But for some people, this takes way too long.
Instead of sitting and waiting, some people force patinas into their blades. They can’t wait to get that beautiful design and rust preventive properties.
If you want to try this yourself, you should go for it! However, I should caution you though that this is a process that can go wrong. You should be very careful whenever you try to force a patina on your blade.
A lot of people have ruined their blades by trying this. That’s why you should take time to consider it first. Think about whether or not the reward is worth the risk.
If you’ve decided to give it a go, great! Let me give you my step-by-step process of forming a patina.
Step 1: Get Mustard
Mustard?? What does mustard have to do with patinas?
Good question. Mustard is naturally acidic. And how do patinas form? That’s right, acids!
Step 2: Coat Knife
It may seem like a strange exercise, but this is one of the best ways to get a patina.
Rub mustard on your blade until it is completely covered. You can also coat your knife in a certain pattern. This way, you’ll get a better design on your blade.
Step 3: Wait
You want a chemical reaction between the knife and the mustard. So wait a while.
I wait around 6-8 hours. The longer you wait, the darker your patina will be. If you don’t want it to affect the blade too much, don’t wait this long.
Step 4: Wash and Dry
Once the time is up, all you have to do is wash off the mustard and dry your blade.
After letting mustard sit on steel for so long, it will cause a lot of chemical changes. And when you wipe off your blade, you will find a patina where once there was smooth steel.
That is the method that I and a lot of others use. But this is not the only way to get a patina on your blade.
If you’re looking for a faster way to do this, you can use vinegar. As we all know, vinegar is highly acidic. That’s why it can get the same effect on your steel a lot faster.
A word of caution: you have to be very careful when using vinegar. If you leave your blade in it for too long, it will destroy the steel.
A slower, but more natural, way to get a patina is by slicing fruits. As you can guess, the acid of fruits will affect the blade. When you use your knife on a lot of fruits, you’ll see patinas forming in no time.
How to Remove Patinas
The results of trying to force a patina can vary. Sometimes, you might get exactly what you want. Other times though, you may get a very messy result that you don’t like.
Or perhaps you are someone who doesn’t like patinas at all. Maybe you’ve been using your knife for a while now, and its starting to form a patina that you hate.
The good news is that there are ways to remove patinas.
One easy way to remove a patina is by using sandpaper. But before you go and sand your blade, make sure you use very fine-grit sandpaper. If you don’t, you’ll end up scratching your blade a lot.
You can also opt for very fine sharpening stones. Whatever the case, you want to polish your blade to remove these patinas.
If you’ve reached this far, you’ve gone from wondering what a patina is, to knowing everything there is to know about it.
With this knowledge, you will no longer freak out when you see a patina. You’ll know exactly how to remove one. And you might just force one into your blades as well.