You may have seen some stunning knives boasting that they're "coreless" from some blacksmiths and wondered what that truly means in terms of construction and performance - here's how they're made and work.
Coreless knives typically fall into two categories;
A mono-steel like the Goko Hamono Kogetsu is one where the entire knife is made from a single piece of steel rather than a traditional core (Hagane) and cladding (Jigane) combination of materials.
2. Combined core steels
The more common coreless style is one where a knife is made from more than one steel like the Sakai Takayuki Coreless range or a Shoichi Hashimoto knife where the steels are typically both a hard core steel so there's no specific core material as they're combined.
You might see a knife like the Sakai Takayuki where they've folded VG2 and VG10 steels together to create the damascus finish or in some extremely high end carbon steel knives from Hashimoto or Nigara Hamono where Blue #2 and White #2 steels have been used. It would be quite normal to see a typical knife that uses any of these steels individually as a core material then clad with a cheaper and softer stainless or reactive material like soft iron to protect the core.
Performance vs art
Most of you will be wondering, is a coreless knife better than a traditional san-mai construction and the reality is that there's little practical difference.
Ultimately the cutting edge of the knife is a core steel that would be appropriate to the knife whether it's VG10, Blue #2 or any number of other choices and the performance and durability of the steel are decided largely by the geometry of the blade and the quality of the heat treat by the blacksmith and the finish applied by the sharpener.
The cladding steel and finish can help with food release but in real terms you won't see significant performance gains from a coreless damascus knife over any other traditionally made knife so it's not unreasonable to say that the primary focus of coreless knives is more for the artistic part although in theory the cladding will be harder and more durable it's a marginal gain.