Let’s start by the ranks of the forging process and the steel. From the top are the ones with the most “kirenaga” or durability.
Honyaki (ao-ko) – Forged out of a single material of high carbon blue #1 steel. This is the highest grade of best japanese kitchen knives. For the true professional only because of the skills needed to sharpen and maintain it. Only used for delicate work like sashimi. Since honyaki’s are the hardest to forge, requiring high level of skills and experience, it is the most expensive. Prepare to fork out at least around $1200 USD (minimum!) for a 33cm yanagi of this rank.
Honyaki (shiro-ko) – Forged out of a single material of high carbon white steel. Just like the ao-ko honyaki but without the tungsten and other additives. It is notably softer and easier to sharpen compared to the ao-ko honyaki. Still, it is very hard (around 63 HRC Rockwell scale) and again, only for the professional due to the skills needed to sharpen and maintain it. As this is a honyaki, it is costly. Prices vary from maker to maker but it usually starts at around $800 USD for a 33cm yanagi.
Kasumi (ao-ko) – All kasumi’s are forged with 2 kinds of steel, solid high carbon steel sandwiched between soft iron. This rank of steel are reserved to experienced chefs who want more durability out of their knives. When it comes to kasumi ao-ko’s, there are 2 grades of it. The harder and more durable blue #1 or sometimes called super blue and the latter blue #2 or ao-ko. Most chefs will argue that the blue #2 is rather the same or just a hair above a good kasumi white steel knife. So how much does it cost you may ask? For a 33 cm yanagi forged with the blue #1 steel (super blue), it may set you back around $500 USD while the blue #2 of the same length around $400 USD. Please do note that some makers refer their blue #2 knives as different names. This is the case with Mizuno Tanrenjo. Their blue #1 knives are called ao-ko deluxe and their hontanren series are blue #2. Make sure you get sufficient information from your maker regarding this grade before you make your purchase.
Kasumi (shiro-ko) – For the novice and professional alike, easy to sharpen and maintain. As mentioned above, all kasumi’s are forged with 2 kinds of steel, solid high carbon steel sandwiched between soft iron. Although this is the lowest rank, it is divided further into a few sub ranks. Names vary between makers but it usually goes like hon-kasumi, kasumi and shiro-ko. Prices and durability vary greatly between makers but I would say anything over $400 for a 33 cm yanagi is not worth getting.
You might notice me repeating the same length for the yanagi’s. Well, that’s the most often used length for professionals when it comes to yanagi knives. Most first time buyers make the mistake of getting a short one because it feels right in the shop and regret later because they wear out fast and it’s too short to make a nice clean cut for sashimi. For Deba (fish cleaver), try getting something at least 21cm. If you have a lot of chopping to do, get the hon-deba. If you have a mix of chopping and filleting, try out the ai-deba. Ai-deba’s are thinner and lighter compared to hon-deba’s. If it’s all about filleting, get the oroshi-deba.
Basically, there are 2 types of steel used in the forging process. The shiro-ko and the Ao-ko (white steel and blue steel). The latter being more superior (and expensive). The difference between this 2 is the tungsten additives in the Ao-ko which makes it notably harder and durable than the shiro-ko. In terms of sharpness, if done properly, the white steel (shiro-ko) can be sharper than the blue steel, this is due to the smaller carbide size of the white steel of around 0.2~0.25 microns. There’s also the damascus if you’re purely into aesthetics. Damascus knife’s are true work of art, it is forged in a way that you can see the intricate patterns along the length of the knife, the sharpness vary due to the many types of steel that can be “damascus” forged.
The choice between the 2 types of steel (shiro-ko and ao-ko) when selecting a knife all depends on what type of abuse you are putting it into. A professional sushi chef won’t have the time to sharpen their knife’s a few times a day so it’s important to have a durable knife that can last him a full day.
All the price range listed here is from Mizuno Tanrenjo, although I get nothing from them for promoting their knife’s, it is still my favorite knife forger after working with different kind of brands in numerous restaurants and hotels from Tokyo to Fukouka. Masamoto is another maker worth checking out. Of course there are lots of great knife forgers out there but this 2 is just my personal favorite.