In this series, we’ll look at the basic definitions regarding the composition, shape and look of knives. Because it’s best to start at the beginning, we’ll first delve into the lamination of blades or, in other words, their multi-layered construction. So, let’s find out more about the properties, as well as pros and cons of various lamination types.
Depending on the manner in which the softer steel (jigane) surrounds the harder core (hagane), we sort lamination in the following categories: 👇
🦉 The knives on our website are also sorted into these categories, so you can browse them by applying the filter on the left side of the collections.
→ One layer of steel
As the name implies, these knives are not laminated but rather made of a single type of very hard steel which is naturally scratch-resistant. A monosteel blade has no pattern on its surface, which is usually polished to a mirror-like finish, and the design is minimalist.
Single-layered or monosteels are further divided into uniformly tempered blades, where the entire blade has the same hardness and martensitic structure, and honyaki blades that involve an older and more romantic manner of knife construction. Actually, fewer than 1% of the knives in Japan are honyaki forged, but the resulting blades are considered by many knife nerds to be the finest on the planet. The honyaki blade is made from one piece of steel and goes through a two-step quenching process. Called differential heat quenching, this process leaves the spine softer so it acts as a cushion like the lamination does in other knives, while the edge acquires a hard, martensitic structure and stays sharp for a very long time.
Because this technique was used by swordsmiths, kitchen knife makers named the process honyaki from the words honmono (genuine) and yakiire (quench). The word honyaki could therefore be translated to “genuinely quenched” and this category includes all knives that are made entirely out of one piece of material, usually classic Japanese steel, but are then put through the process of differential heat quenching which leaves the edge very hard, while the spine of the knife, though the same piece of steel, is softer and protects the blade from breaking. This technique is difficult to perform and perfect, thus only the most experienced master blacksmiths make the honyaki knives. Being exceptionally rare, expensive and delicate, they are suitable only for highly experienced chefs. They are greatly appreciated due to their kirenaga or edge retention capabilities, maintaining sharpness for a very long time.
They can be either ground on both (double bevel) or just one side (single bevel).
The kitchen katana: How a famed samurai sword came to be used on a chopping board
Most Japanese knives are made with a hard steel core surrounded by a softer steel laminating either one or both sides. Honyaki knives, however, are made from one solid piece of high carbon steel. If the entire blade would be quenched in the same way, it would be extremely fragile and could get damaged devastatingly quickly. Japanese blacksmiths encountered this problem when forging katanas and found a solution: differential heat quenching. When a knife is forged and roughly sharpened, instead of evenly coating the blade with clay as with other knives, a blacksmith would put a thick layer of an insulating paste, which is made from clay, carbon, dust of natural sharpening stones and water, on the spine. The blade is then water quenched and it is during this stage that the katana acquires its characteristic curvature. The uncovered part of the knife cools rapidly during quenching and crystallizes into a martensitic structure. The steel becomes hard which is of key importance for retaining an edge. The other part of the knife, covered with a thick layer of paste, cools down more slowly and crystallizes into pearlite, a less hard and lamellar mixture of cementite and ferrite. The result of differential heat quenching is therefore a knife that is composed of one type of steel and two different crystal structures. A line that forms between these two structures is called the hamon. By correctly using the traditional technique of sharpening and polishing, the hamon line between the two crystal structures can be exposed and itself become a true work of art. Because both parts of the manufacturing process are so important and specific, usually both the blacksmith and the sharpener who were involved in making a honyaki blade are named.
In the past, this process of forging and quenching was used to make the samurai katanas, while today it is being applied to produce perhaps the most beautiful knives you will ever see. Among the sushi masters, a Honyaki Yanagiba is a status symbol!
→ Three layers of steel
→ San-mai knives are always double-beveled
San-mai translates to “three layers” and, in this construction, a softer steel is forge-welded onto either side of hard steel core, giving the blade a structural integrity without sacrificing its ability to hold an edge. This method allows for easier manufacturing (especially quenching) and also easier sharpening. The blade is therefore composed of a primary, inner layer and of two secondary, outer layers. An important aspect is also the type of steel that is used for these layers. Very often the primary layer is made of steel with a high carbon content (and is prone to corrosion) and is then sandwiched between two layers of stainless steel with a high chromium content that protect the delicate core from external factors such as rust and breakage.
This is by far the most common practice of manufacturing Japanese knives.
🦉 The first blacksmith who invented the lamination of rust-prone and stainless steel was Teruyasu Fujiwara san, the Japanese legend among contemporary blacksmiths.
→ More than three layers of steel
→ San-mai knives are always double-beveled
San-mai Damascus steel represents the highest art of bladesmithing. The central core of the blade (cutting edge) is made with a harder steel and wedged between more than two layers of milder, more pliable steel. The result of this process is Damascus steel, which is laminated in the san-mai style, but includes more than five layers (always an odd number). It is sometimes called suminagashi because it gives the impression of marbling on paper.
The rippling Damascus pattern doesn’t have a function in itself because a central core and two outer layers make up a perfectly fine knife. These multiple layers therefore represent an additional aesthetic value, along with a higher price tag, and blacksmiths use it to display their artistic flair and show off their talent. But don’t be fooled: behind the scenes they draw from a wellspring of centuries-old heritage and hard-earned knowledge, many hours of work and substantial amounts of material.
Damascus is formed by layering different types of metal alloys together, then forging them into a single piece. When these alloys are sharpened, when they come in touch with acid or when they’re bead blasted, they respond differently and reveal visually striking patterns.
The blade can be treated in various ways:
- Acid etching: the layered metals react to the solution in different ways. For example, carbon steel, which is less resistant to corrosion, darkens, while nickel silver remains bright. The alternating layers of darker and brighter metal help reveal the flowing, rippled pattern.
- Bead blasting: blasting the steel with abrasive material means that a softer steel takes on a matt look, while harder steel retains its luster. It also provides surface textures to help food release from the blade and to reduce cutting drag. Bead blasting is usually used to obtain a more subtle Damascus pattern.
- Sharpening/polishing: the patterns and mechanical differences between steels can also be brought out by sharpening them with whetstones.
- Combination of methods.
The mystery of Damascus steel
Damascus knives can be instantly recognized by the unique, beautifully undulating lines that adorn the blade. This characteristic pattern is the result of laminating various layers and types of steel. However, we shouldn’t confuse damascene patterns on modern knives with Damascus steel that was used to forge swords and other weaponry.
Because up until the pre-industrial era it was not possible to produce a homogeneous steel with metallurgic technology, the blades were manufactured from several welded layers of softer and harder materials. First Damascus blades were developed simultaneously in various parts of the world around 3rd century B.C. In Europe, Damascus swords were being made, while a similar technology was used to produce Japanese katanas. These blades were lauded for their durability, resistance to breaking and superior sharpness. It was said that they could cut through a silk scarf as it fell or split a feather in midair.
The original formula for producing this type of Damascus steel has been lost to history. The striking texture, however, is being successfully reproduced with advanced technology, procedures and materials. Considering the technology of the time, Damascus blades were extraordinary. Their properties were unique and combined super plasticity with incredible hardness and an unbeatable strength with durability. This is also why it was long thought that it has mystical qualities. The fascination with the mythical Damascus steel exists and, even today, beauty has its natural place in the world of steel.
Ni-mai and Ni-mai Damascus
→ The lamination of single bevel knives
Ni-mai lamination is used in knives that are ground only on one side and are composed of a hard core (cutting edge) and a softer, external layer. If the softer layer has several layers of steel, it is called the ni-mai Damascus lamination where the pattern can be seen only on one side of the blade (usually the right side because the majority of single bevel knives are intended for right-handed users). Due to soft and pliable external layer of steel, the sharpening of single bevel knives is much easier.
→ This method is usually used only on double bevel knives
The hard core of a knife is sandwiched between two layers of softer steel, reaching only up to a half of the blade’s width. This specific type of construction is used for steels that are very challenging to forge, for example for certain types of powder steels. A glowing hot piece of iron is split and a piece of steel is inserted. The new material is now forged into one piece. This creates a highly durable kitchen knife with a slightly more pliable core. The main advantage of these knives is that they are thin, sharp and retain their edge very well. Warikomi is also called the “split and insert method”.
→ This process of forge welding is also called pattern-welded Damascus
The pattern-welded steels are produced by forge welding alternating sheets of steel which are then folded and forge-welded together numerous times. During this process, an attractive surface pattern emerges: swirling patterns of light-etched regions on a nearly black background. This is an extremely complex and lengthy process, therefore these knives are really rare and belong to the group of highly sought for and expensive knives.