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After using your high carbon steel knife for a while, you will notice the steel loses some of its shine and seems to become stained from the materials it was used to cut. This is what is known as patina. Is patina a good thing or a bad thing on a knife, and should you force a patina or take steps to prevent it?
Patina is a form of oxidation on the metal surface of a high carbon steel knife. Unlike rust, it is not corrosive but forms a protective barrier on the metal and helps prevent rust. You can let the patina develop naturally or force a patina, but you should not prevent it from happening.
Many people new to high carbon steel knives are a little perplexed when they see a patina developing on their expensive knives. They are not sure if it’s a problem that could damage the knife and whether it should be removed or left in place. We will clear up this issue for you and show you how to force a patina on the knife to use this form of oxidation as protection for the blade.
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What Is Patina On A Knife
Many first-time owners of carbon steel knives become dismayed when they see the lovely shiny steel blades becoming tarnished and discolored with use. Many people think they have done something wrong or have not taken proper care of the knife.
This is not the case, and if you are in this position, you can rest assured that the tarnish on the blade is not due to your mistreatment of the knife.
Patina is a form of oxidation that occurs on the surface layers of the steel when the knife is used and comes into contact with the items you cut. You will notice that the blade discolors quicker when you use the knife to cut acidic foods or ingredients.
This is because the patina is not a reaction of the steel to air and moisture but rather to the acid in the food.
The acid reacts with the upper layers of steel on the knife’s surface, oxidizing the surface and leaving a layer of oxidation on the steel, which we see as a stain or discoloration on the blade.
Patina is not rusting and will not eat into the steel and damage the blade as rust does. The layer of oxidation of the patina actually serves to help prevent rust from developing on the steel.
This is why many knife makers force a patina by etching their knives in a weak ferric chloride acid, which darkens the steel with an oxidation layer and helps to prevent rust.
Stainless steel does not naturally patina, and a patina cannot be forced on knives made from this steel. The stainless nature of the metals included in the steel makes it resistant to rust as well as developing a patina, which is considered a stain.
Should I Prevent Patina on a Knife? No!
The most common reaction for people discovering a patina on their knives is to try and clean the patina off and prevent it from occurring on the knife.
Trying to prevent the patina from developing on the knife blade will be very difficult. It is a naturally occurring process that will happen whenever you use your knife on acidic foods.
Unless you plan to refrain from using your knife on acidic ingredients such as tomatoes, pineapples, and the like, patina is bound to happen.
Even taking protective measures such as wiping the knife off, or washing it immediately after using it, will not prevent the patina from happening.
You should not actively try to prevent the patina from occurring since the oxidation layer that results from the patina is beneficial to the steel in helping to prevent rust, which, unlike patina, will damage your knife.
Some people try to remove the patina by resorting to scrubbing the knife with harsh chemicals, such as ammonia-based cleaners and steel wool. Trying to clean the blade in this way will do more harm to the knife than leaving the patina in place.
In summary, you should not try to prevent patina on your knife blade, and you should not try to remove it either!
TIP: You may have heard of knife blade coloring. Is painting a knife blade just a decoration or can be protective? Check out the explanation in the article below:
Painting a Knife Blade: Decoration or a Protective Coating?
Should I Force A Patina On My Knife
The next question is the other side of the patina coin. Should you force a patina on your high carbon steel blade, or should you wait for it to occur naturally at its own pace?
It is not an absolute necessity to force a patina on a knife. The patina that occurs naturally will perform the same function but will take a little longer to form.
Some people prefer the aesthetic of a naturally occurring patina to the look of a forced patina. Conversely, others prefer the look of a forced patina because it allows some creativity in forming the patina or a more even patina across the entire blade surface.
Forcing a patina is not essential, and it is entirely the personal preference of the knife owner, but it can have some benefits.
Why Force A Patina On A Knife?
It is unnecessary to force a patina on a high carbon steel knife, but it is also not a bad idea either. Forcing the patina of a knife can offer the following benefits.
- Immediate protection of the steel. Forcing a patina will place the protective oxidation layer on the steel immediately and protect it from rust.
- An even patina. A forced patina will cover the blade evenly, which may be more aesthetically pleasing for some people.
- Allows for creativity. A forced patina allows for some creativity in the formation of the patina in the way of patterns and designs and different shadings or patina.
Many knifemakers supply the knives with a patina already in place, but if you have a high carbon steel knife without a patina, you can force a patina yourself.
The process is not very complex or difficult, but some care must be taken to prevent damaging the knife during the process.
BTW: If you want to know more about Japanese and other knives and their sharpening, check out the books listed above. These books are recommended by professional sharpeners and knife makers (Amazon links):
- Japanese Kitchen Knives: Essential Techniques and Recipes
- The Knifenerd Guide to Japanese Knives
- Knife: The Culture, Craft, and Cult of the Cook’s Knife
- Sharp: The Definitive Introduction to Knives, Sharpening, and Cutting Techniques, with Recipes from Great Chefs
Best Way How To Force A Patina On A Knife Blade
It is possible to force a patina on a knife, even if you are not a knifemaker with all the tools and equipment to get it done professionally.
A home patina can be successful, but it will fade and wear off over time and with the use of the knife. A home forced patina may need to be re-done on the knife from time to time.
The best way to put a patina on a knife blade is with a dilute solution of ferric chloride. This is an acidic chemical that knife makers use to etch a blade and provide a patina on the surface. A ferric chloride etched knife has a dark, durable patina evenly distributed over the blade.
TIP: If you are interested in buying ferric chloride we recommend buying this one by MG Chemicals (Amazon link).
Ferric chloride is also the chemical of choice for knife makers to use to get the patterns of Damascus steel to stand out.
The different metals in Damascus react to the acid differently, creating shades of light and dark, which follow the pattern of the different steels in the blade.
As a knife owner, you may not have access to ferric chloride and may not be interested in purchasing this chemical for the limited number of times you will use it.
In this case, you can use other methods to achieve a forced patina on your knives, often with standard household ingredients already in your kitchen cupboard.
TIP: Taking proper care of your knives can be difficult. One of the frequently discussed questions is about electric sharpeners. Do they ruin your knives? Find out the answer in the article below:
Explained: Do (Electric) Knife Sharpeners Ruin Knives?
How To Patina A Carbon Steel Knife
One of the easiest methods to patina a knife at home is using vinegar as the etchant. There are several methods, each using different types of vinegar. We will detail a couple of options here that you can try at home to get a good patina on a knife.
Using white vinegar is the first method we will detail to patina your knife. The supplies you need to do this job are probably already in your kitchen.
Gather the supplies in the following list in preparation to patina the knife (Amazon links below).
- Denatured alcohol. The alcohol is to clean the knife blade before creating the patina.
- A glass jar. The glass jar must be tall enough for the knife to stand blade down in the jar so that the entire blade is in the jar, but the handle sticks out. Glass will allow you to observe the process taking place without the need to pull the knife out every few minutes.
- A bottle of white vinegar. Any white vinegar will do.
- A bottle of Windex. This will be used to neutralize the acid
- A clean cloth. The cloth will be used to wipe the blade down.
- Mineral oil. To protect the knife from rusting.
Before starting the patina process, use the cloth to thoroughly clean the blade with the denatured alcohol. This will remove any fingerprints and other contaminants which could affect the quality of the patina.
The steps to patina the knife are pretty straightforward, but you need to monitor the process carefully to prevent the vinegar from eating deeply into the metal.
- Pour the vinegar into the glass jar. Pour enough vinegar into the glass jar to cover the entire knife blade, ensuring the vinegar does not touch the knife’s handle.
- Place the knife in the vinegar for 5 to 10-minutes. Stand the blade in the vinegar for at least 5-minutes. The longer it is left in the vinegar, the more it will darken. Do not leave the knife in the vinegar longer than 10-minutes. The acid could start to eat the metal away. It is better to do multiple, short soaks in the vinegar rather than one long stretch.
- Extract the knife and clean it off with Windex. Take the knife out of the vinegar, spray it down with the Windex to neutralize the acid in the vinegar. If you don’t have Windex, you can rub baking soda on the blade to neutralize the acid.
- Rinse the knife off. Rinse the knife under clean running water to wash off the vinegar and Windex. Dry the knife thoroughly.
- Examine the patina. Examine the knife’s blade to see if you are satisfied with the outcome of the patina. If you are happy with the level of patina, move on to the next step; otherwise, repeat steps 1 through 4 until you are happy with the outcome.
- Wipe the knife down with mineral oil. After the final wash of the knife, wipe the blade down with mineral oil to prevent rust.
Another method you can use is with apple cider vinegar and a paper towel. This method does not need the glass jar, but the other items will be required.
- Soak the paper towel in the apple cider vinegar.
- Wrap the vinegar-soaked paper towel around the blade.
- Leave the paper towel on the blade for 5-minutes.
- Remove the paper towel and clean the blade as per steps 3 to 5 in the procedure above.
The paper towel wrapping method adds interesting patterns to the patina imparted to the knife’s blade. If the etching is not as dark as you would like, repeat the process, finishing by washing the knife, drying it, and giving it a coating of mineral oil.
TIP: Japanese knives are the most popular type of knives around the world. Do you know why some of the Japanese knives have grooves or dents? Find out the answer in the article below:
3 Reasons Why Japanese Knives Have Grooves Or Dents
How To Put A Mustard Patina On A Knife
Another popular method to patina a knife at home is to use mustard as the etching agent. The type of mustard is important since it is not the mustard that does the etching, but rather the vinegar in the mustard.
The semi-liquid mustard like you would put on a hotdog is the mustard required for the process. These mustards contain vinegar, as indicated in the list of ingredients on the bottle.
The first step is to clean the knife thoroughly. You can use denatured alcohol or acetone to clean off any residual oil and grease from the blade.
Spread the mustard over the blade’s surface in a pattern of your choice. You can cover the entire blade, but the mustard patina will not be as effective over the entire blade as the plain vinegar method.
The mustard patina will create dark lines around the edges of the mustard. The parts covered by the mustard will darken slightly, but not as dramatically as with the vinegar patina. The reason for this is that the concentration of vinegar in the mustard is very low.
Leave the mustard on the blade for 30 to 45-minutes, then wipe it off with a cloth. Spray the knife down with Windex to neutralize the vinegar. Wash the knife and give the blade a coating of mineral oil.
Creating a patina on the knife with mustard is generally intended to create patterns on the blade rather than cover the entire blade. This method is often used to put a fake Hamon on the blade.
If you want to have a pattern on the blade, use the mustard method and then patina the entire blade using the initial vinegar method we described. The existing lines from the mustard method will darken even further during the vinegar treatment.
A patina on a knife is not a cause for concern. The patina forms a layer on the knife that protects the steel from rust to a certain degree.
You can force a patina on the knife, but this is not necessary but rather a personal preference. A naturally occurring patina will perform the same task. A forced patina simply gets you there sooner and gives you some control regarding the patina’s look!
TIP: Patina is not rusting. You want to force a patina on your knives but prevent rusting. Check out the step-by-step guide on removing rust from Japanese knives in the article below:
Removing Rust From A Japanese Knife In 5 Steps (+ Prevention)