Patina on a knife, on steel or other types of metal is something about which we receive many questions. For example, there are people who wonder what the strange stains on the blade of their expensive chef’s knife are all about. Or a gray cast on an outdoor knife made of carbon steel. Rust is often immediately thought of. This is not always justified. We are therefore happy to explain what patina is, but also what the advantages and the most important points are.
What is Patina?
Patina is a broad term that we believe can be described as evidence that a product has a certain “age”. A type of wear and tear. Natural, superficial discoloration of a metal that lies on the surface like a kind of layer.
Patina usually forms on knives made of carbon steel. Think of survival knives made of 1095 carbon steel, for example. But also on kitchen knives. Eden Kanso Aogami knives, for example, are known precisely for forming a beautiful patina.
There are also sometimes big differences visible between grades of carbon steel or tool steel. This is due to the different gradations of rust resistance. Some grades of steel have absolutely no resistance to corrosion and will create a patina just by holding a finger against it. Other grades need to be exposed to the elements for a longer period of time, and then eventually show discoloration after a few weeks or months.
Otherwise, a patina can of course show up on other materials as well. For example, brass, copper, and bronze. These metals can tarnish black or even green. For example, a Buck 110 may have a flawless blade, but the brass bolsters show the true age and character of the knife.
How does a Patina develop?
Patina can form in a number of ways due to external influences. You can expose two exactly the same knives to different conditions, and you will see them discolor in different ways. Known catalysts of patina are Salt, acid, and moisture.
Effects of salt and moisture are almost inevitable. As soon as you touch a carbon blade with your fingers, the transpiration on your fingers already begins its effect. For example, you can often see a dark gray color cast around the thumbhole of some Spyderco Sprint Run pocket knives made of exotic tool steel grades after a few weeks of use. No need to worry: simply patina.
What is the Function of Patina?
Over time, you will notice that with a normally formed patina layer, the blade will one day become less susceptible to rust. Do you notice at the beginning that your carbon steel kitchen knife already gets stained and discolored when you wash it immediately after cutting? Then, after a while, you will suddenly notice that the blade actually permanently retains its existing discolorations. The patina then acts as a kind of “seal” on the steel.
In the meantime, the blade already has discolorations and stains that make the knife unique. Thus, the knife becomes yours not only in terms of ownership but also in terms of charisma. The knife gets a character and shows what you have experienced together with him.
What is the Difference between Patina and Rust?
When you hear that patina forms on knives that are not so rust-resistant, you might almost think: But then it’s rust? However, it is not that simple. Patina is a thin layer that forms on the blade and is eventually “finished”. Whereas rust, on the other hand, just won’t quit and eventually attacks the steel. The line between the two is thin, but the patina is really more controlled than the rust.
How do you form a controlled Patina on a knife?
Just because you like to build a patina on your carbon steel knife doesn’t mean it’s okay to neglect it. You need to use and clean it normally, as you are used to. The patina will come all by itself. That’s why it’s also extremely important to dry the knife really well after cleaning it.
It is undoubtedly a common mistake with kitchen knives to quickly dry a Japanese carbon steel knife with a dish towel that is a tiny bit damp. The knife will then simply not dry completely. Try it once and take a critical look at the surface of the blade. You will then see that in many cases the surface has remained slightly damp. Do you put the knife away in this condition? Then you are challenging real rust.
In Japan, cooks use two dishcloths for this reason: one that is allowed to get slightly damp to absorb most of the water while helping to clean the steel well. And also a tea towel that stays as dry as possible for careful drying of the blade.
How do you force Patina on a Knife?
Don’t feel like taking excellent care of your knife in the first few weeks to prevent rust? Then you can give nature a helping hand. Some people decide to smear the blade with mustard. This is so acidic that the patina forms in a rush. Within a quarter of an hour, you will see the result. This way you can even form artistic patterns on the blade.
An important disclaimer applies here – it’s already a bit of a game with fire. Did you leave it on too long? Or is the result a little too extreme? Then you can always take care of rust.
How do you remove the Patina?
Does the knife no longer look quite the way you wanted it to? Did you go a bit too far in forcing patina, or would you rather start over? Then you can often remove the patina pretty easily. Some people swear by having it sanded clean flat on a Japanese water stone. But then you should know well what you are doing. We ourselves are fans of a cleaning cloth with some Flitz. With that, you polish the layer away. However, it is good to know that the result can always be different from the condition in which the knife was delivered new.