Introduction of Aogami, highly ranked material for Kitchen Knives
We are going to share with you about “Blue Paper Steel”, the highly ranked material for cutlery steel known as “Aoko” or “Aogami” in Japanese.
“Aogami” is an alloy steel made of Shirogami (or called “White Paper Steel”, a carbon steel with low content of impurities), mixed with tungsten and chromium, which means Aogami is a steel made by the hands of human. Among others, what matters the most is how sharp a knife edge can be and how long its sharpness can last. Plus, if it doesn’t take much to sharpen the edge, that’s fantastic. Some says that Aogami was used for an aim to achieve these features, while the material was originally developed for an edge of plane for shaving a wood pillar in Japan.
First, we’d like to touch on the definition of “Blue Paper” Steels, or “Aogami”. There are three kinds of Aogami; “Ao-ichi ko (Aogami No.1) “, “Ao-ni ko (Aogami No.2)”, and “Aogami Super (Blue Paper Super)”. There are two types each for Aogami No.1 and No.2; Aogami No.1 A and B, and Aogami No.2 A and B, meaning 5 kinds of Aogami in total which are used for cutlery steel. steel.
Second, we’d like to consider the differences between A and B of Aogami No.1 / No.2. ‘A’ is a steel material used for a hard edge knife so called “katakuchi hamono” in Japanese while ‘B’ for a less-hard edge knife called “amakuchi hamono” in Japanese.
The difference between A and B comes from the amount of carbon contained within. The more carbon, the harder a blade can be. Other than the amount of carbon, the remaining ingredients are all the same, meaning that the only difference between A and B is the amount of carbon. If a blade is hard, it can cut food well. At the same time, it needs to be paid attention because it is prone to form rust and chip off.
The Blue Paper Steel has a high level of stickiness and abrasion resistance thanks to chromium and tungsten, so it can keep you from worrying about chipping-off and wearing-out of a blade to some extent compared to White Steel. Since the Blue Paper Steel contains a certain level of carbon, rusting and chipping are inevitable. We can’t tell the difference between A and B just by looking at them but we can by using and sharpening them. Also, the level of hardness varies depending on quenching and tempering temperature. Plus, depending on the skills of a blacksmith, A’s level of hardness can be as the same as B’s.
It must be noted that “Aogami Super (Blue Paper Super)” is NOT necessarily the best in the 5 types of Aogami, sometimes the worst contrary to the hardness and price unfortunately.
Aogami No.1 (Blue Paper Steel No. 1)
As basic information of Aogami No.1, it contains a high amount of carbon, and higher amount of chromium and tungsten than Aogami No.2. For this reason, the price tends to be more expensive than No.2. Because of its stickiness and abrasion resistance, Aogami No.1 is highly recommended if you look for top-notch quality cutlery in the Aogami series.
One thing that should be noted is that it is highly likely that you feel slippery when you hold a knife and try to cut something due to high content of chromium. You can solve this issue by using a finishing whetstone which gives a bit rough touch. If you currently use No. 8000 whetstone, you can replace it with No. 6000.
By doing so, it adds sharpness to a blade as if it literally catches and bites food. If you are a skilled and experienced chef, even using No.10000 to finish the blade to the extent that it can be slippery, you should be able to treat and cut food beautifully.
A lot of people may pause to question, “Why does a rougher whetstone need to be used? We are talking about a blade of cutlery. Shouldn’t it be sharp enough to cut food very smoothly?”
When a chef using a knife feels a sense of sharpness of its blade, it simply means that the edge of the blade is rough as a micro saw, which consequently gives cut end of food rough finish. It’s true that it’s less efficient in cutting Sashimi with a knife finished with a rough whetstone.
*Phosphorus and Sulphur are chemical components affecting sharpness, and Japanese popular metal maker — Hitachi Metals — strictly gives control over them in their products.
What is Aogami No.1-A ?
Aogami No. 1-A contains 1.30-1.40% carbon of total ingredients. Due to its quenching and hardening properties, the blade can be sharper than that of “Aogami No.2”. On the other hand, its hardness may make sharpening difficult and therefore cause rust often. From theoretical viewpoint, the blade made of Aogami No.1-A can cut very well and its sharpness can last.
What is Aogami No.1-B ?
Aogami No.1-B contains 1.20-1.30% carbon of total ingredients. It’s less hard than the Aogami No.1-A, but has more sharpness compared to the Aogami No.2. Due to its less hardness, a blade of finished product tends to be a bit soft. When you purchase an Aogami No.1 knife, you will have this Aogami No.1-B. It may be easier for us to handle and care for this No.1-B compared to No.1-A.
Aogami No.2 (Blue Paper Steel No. 2)
As basic information of Aogami No.2, it contains a lower amount of carbon, chromium and tungsten than Aogami No.1. It’s less expensive than Aogami No.1, so its hardness, stickiness and sharpness is one step behind Aogami No.1. Having said that, it would be best for those who want to purchase their first Aogami Steel cutlery since it is regarded as an icon of Aogami cutlery with ease of use. Therefore Aogami No.2-B is often considered as standard in evaluating Aogami Steel.
What’s Aogami No.2-A ?
Aogami No2-A contains 1.10-1.20% carbon of the total ingredients. As you can see the difference in the amount of carbon between Aogami No.1 and No.2, No.2 is a steel with a lower level of hardness compared to No.1. It is unlikely that you come across Aogami No.2-A products in the current market. Even if Aogami No.2-A is used for making a knife, it can be degraded into Aogami No.2-B or lower in case carbon comes off while manufacturing (decarburization).
What’s Aogami No.2-B ?
Aogami No.2-B contains 1.00-1.10% carbon of the total ingredients. This Aogami No.2-B is a representative of Aogami No.2 products, and manufactured and distributed the most. From manufacturers’ perspective, Aogami No.2-B is easy to handle in heat-treatment process since its quenching temperature is used as reference for all Aogami No.2. In other words, it can be said that a skilled blacksmith has been handling Aogami No.2-B so many times that they are most sensitive to the feeling of it.
When the amount of carbon changes, so does tempering /quenching temperature to some extent. Such a slight difference in the temperature influences perfection of a finished product, Hocho (“kitchen knife” in Japanese).
Aogami Super (Blue Paper Super)
The hardness level of a blade of Aogami Super knives may go up to around 70 HRC at the moment when a blade is quenched, and then is to be set back to 65-68 HRC by tempering. Still it is harder than any other carbon steel and it simply means that a finished product requires less frequency of sharpening. Also, its hardness and stickiness can protect a blade from abrasion, keeping it from being thinner.
The amount of carbon contained in the Aogami Super accounts for 1.40%-1.50% of total ingredients. It contains the same amount of chromium and tungsten as Aogami No.1 while it does have molybdenum and vanadium with high content of carbon. Molybdenum has properties to increase stickiness more than chromium, leading a knife to keep long-lasting sharpness. Vanadium can be a factor to make a steel material that is hard with an excellent abrasion resistance and little flection.
It simply means that a finished product requires less frequency of sharpening. Also, its hardness and stickiness can protect a blade from abrasion, keeping it from being thinner.
Applying mirror finish to both front and rear surfaces can make a finished knife not only rustproof but also durable.
We must note it also has some downside. We’ve just talked about the upside features of it such as long-lasting sharpness, hardness and little abrasion, but if we take the opposite point of view…. Let’s say, if a blade chips off, it takes so much for us to re-sharpen it. If a process of Honyaki (true-forging) is skipped in handling this material, it’s inevitable to consume tremendous time and effort for repairing. Immediately after a blade chips off, its outstanding upside such as hardness and little abrasion turns into a big pain in the neck, gnawing at your energy just for repairing. It also requires a lot of work for blade edging. Even if an idea of making it Meretrix-shape occurs to you, you may know that it may take more than twice the time you expect. If you still want to buy Aogami Super with all these things considered, it’s ok and you’ll be happy with your choice.
Summary of Aogami
Different kinds of Aogamis (Blue Paper Steels) have been covered so far.
It’s sure that the hardness level of a blade of Aogami knives that are currently in the market is over 60 HRC. The moment when a blade is quenched, the hardness level soars to over 65 HRC. Then, the level is to be set back to around 61 HRC by tempering. It would be very difficult to sharpen a blade with an artificial whetstone once the hardness level goes up to over 63HRC.
If you are a skilled chef, you should be able to appreciate and enjoy an Aogami knife satisfactorily with “Aogami No.2-B”. It can be proved by the fact that the most selling Aogami item is “Aogami No.2”. As next step, you could upgrade your cutlery to Aogami No.1. You can bring out the best in Aogami No.1 just because you have taken all its downside features into account and thus will be able to use Aogami well as your strong tool.
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Thank you for reading and best regards!
All the Hocho-Knife staff
“Hocho” represents Made-in-Japan (Sushi / Sashimi) Kitchen Knives,
that is the soul of the cook!
Kyoto and Hyogo, JAPAN