Once you look at it, you will never call it blue paper steel again. It is the material that makes up most of your kitchen knives – but have you ever thought about how it is made, what kind of steel it actually is, or why there are so many different kinds?
You might be surprised to hear that this-there is only one kind. Well, maybe it is more like seven or eight kinds-it can get confusing. It has the name because of the way it looks and feels – much like blue jeans, and paper (which also can be confusing).
So to make things less complicated, we will just call them by their individual names: Blue steel, white steel, blue paper steel, white paper steel, San mai, and Shiroko.
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There are several methods to produce these steels. One of the most common is called Tamahagane -the Japanese term for “Sacred/Pure/Honorable metal.” The Japanese way of making them has not changed in over 800 years.
They call it ” Kō Shitsu Gane” (literal translation: “hot factory steel”) because the process starts with iron sand inside an extremely hot furnace, and they use very pure iron sand that is almost like powder-it heats up so fast you can see it turn red in the blaze of the fire.
There is a lot of labor and a high standard needed to make this steel, which is why it remains expensive. The master smiths take the iron sand and mix it with charcoal from straw or other plant material, then fine sift through several screens to create different-sized particles.
They spread the mixture onto an iron plate in a very thin layer and heat it in the furnace from above and below with charcoal for ten hours.
Then, they add more layers of iron sand and charcoal to make it thicker, never allowing the temperature to go over 800 Celsius (or 1472 Fahrenheit). This process is repeated between thirty-two and one hundred times.
The more times it is repeated, the more carbon will be infused into the iron sand. After all of this, when Metal becomes steel after it was once a sandstorm!
The crystal structure of steel is altered during this process, making it stronger and more flexible. Metal becomes steel after it was once a sandstorm!
The crystal structure of steel is altered during this process, making it stronger and more flexible. This entire process takes thirty-two hours by itself (about two days).
Once the steel is ready and cooled, the master smiths will re-heat it and suddenly slam a large bar of iron into it with a loud bang. This causes the crystal structure to change again and makes the metal very hard. The more banged they do this, the harder the steel becomes.
Now that you understand this process, you can recognize the different types of blue steel. The first is called Hagane, which is pure steel with no additives to it at all. The second is called Kō-hagane, and this has a small percentage of carbon added to it for a harder blade that will not break easily.
Then there is Chi-hagane, which has the least amount of carbon added and is used for knives that need a very sharp edge, but not much durability.
Now you know what they mean when someone says “blue steel.” Blue paper steel is exactly the same thing except it has a small percentage of chromium mixed in with the iron sand. White paper steel is the same as blue, except it is made with clay instead of charcoal.
The one you are most familiar with though is Shiroko, which has no pure carbon in it at all. It is very common steel that makes up many knives and tools that you use every day – but have you ever thought about why it is so strong?
It is because of the clay used to make it.
White paper steel also has clay mixed into it, but not as much as Shiroko does. Depending on how much chromium or iron there are in these steels determines what color they will be at the end – blue, white, black, purple, etc.
So, now you have a better understanding of the most coveted steel in Japan. The pride these master smiths take in their work is enormous and they put a lot of time into it. It outlasts all other types of steel too -which is why these knives are so hard to come by and so expensive- use them with care!
Higher quality Japanese knives are made with blue steel because it is one of the highest quality steels, but it takes a lot of time and effort to make. A single blade can take 32 hours just to create by itself! Different types of blue steel have slight variations in their names, but they all contain iron sand infused with carbon.
One of the most popular is called Shiroko, which also contains clay for a thin layer around the blade to make it even stronger. Master smiths take a lot of pride in their work and outlast all other types of steel because it takes so much time to make them.
Blue paper steel has a small percentage of chromium mixed with it, which makes for a hard and sharp blade.
The more times you repeat the process, the more carbon will be infused into the blade and make it harder. However, after each time they add extra charcoal and iron sand to thicken it up again before another 32 hours of heating. It is because of this that Japanese blades are so strong and last so long.
White paper steel is made with clay instead of charcoal for a thin layer of additional strength around the blade. It has a small percentage of carbon added to it, which makes it stronger than other types of knives but not as high quality as blue steel. Lastly, there is Shiroko paper steel which has no pure carbon in it at all.
It is one of the most common steels used for Japanese blades, but its strength comes from having a higher percentage of chromium mixed with the iron sand. The process can be repeated multiple times to increase how much carbon gets infused into it and makes the blade stronger every time.
White paper steel also has clay added instead of charcoal, which gives it a different type of strength from the chromium mixed into the blade. All three types of blue steel have been practiced in Japan for centuries from master blacksmiths to this day.
It takes a lot of time and effort to create these blades because they are made with such high-quality materials, which is why Japanese knives are so expensive and highly prized.
They continue to be a tradition in Japan because of their strength and durability, proven over hundreds of years. Master blacksmiths take pride in creating the highest quality blades with blue steel, a tradition that has carried on for centuries from one generation to the next.
The strength behind these knives is due to the clay added to the iron sand infused with carbon, which makes them incredibly strong and one of the most sought-after steels in Japan. They are crafted by master blacksmiths who take pride in their work and put a lot of time into every single blade – even more reason why Japanese knives are so expensive.
The percentage of chromium mixed into the blade determines what color it will be at the end – blue, white, black, purple, etc. White paper steel is slightly less durable than blue steel but more so than Shiroko paper steel because of its clay layer added instead of charcoal to strengthen it.
Although there are three types of blue steel used for Japanese blades each one has its qualities and uses, which is why they are so highly prized. Japanese knives use blue steel to make high-quality blades that last a long time, making them some of the best around.
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