A knife description can name a joining process and a number of layers in the same line. Read those as separate pieces of information. TOJIRO's materials reference offers a way to distinguish how a composite material is made from the layer count attached to it.
Technique and structure
TOJIRO describes clad material as different materials joined together and then forged or rolled. Joining is therefore a manufacturing question as well as a matter of how many layers appear in a description. The maker identifies carbon movement between materials as a difficulty at the joining stage and calls its DP method an internal decarburization prevention method. This explains what the process name addresses: carbon loss within the joined material. A layer count answers a different question and, on its own, does not identify that joining method.
Read the materials before the number
The reference discusses joining steel and stainless steel through the maker's DP method. Its examples include 37-layer DP Kasuminagashi steel and 63-layer nickel Damascus steel. These are examples in a technical article dated July 12, 2019; they do not establish the specification or availability of a particular knife offered today.
The useful reading order is to identify the materials being combined, then check any named joining process, and finally read the layer count. This keeps a numerical description from standing in for the rest of the construction information.
Keep hardness separate from the layer count
TOJIRO explicitly notes that hardness and related properties vary with the materials combined. Its general clad-material table therefore supplies no single HRC value. Treat a layer count as a construction detail, and look for a model-specific hardness specification if that matters to your selection. This guide makes no cutting-performance ranking from the number of layers.
For international readers
When comparing translated listings, ask which materials are combined and what manufacturing process the maker actually identifies. A shared layer count alone is insufficient evidence that two knives use the same joining method. The 2019 examples here explain terminology; check current product specifications separately before purchasing.
日本語
クラッド包丁の構造：層数だけでは分からない接合方法
藤次郎の2019年7月12日付材料解説を基に、クラッド材の接合方法と層数を分けて読みます。同社は異種材料を貼り合わせ、鍛造または圧延で作る材料と説明しています。接合時の炭素移動を課題に挙げ、DP法を「内部脱炭防止法」としています。鋼とステンレス鋼の接合や37層・63層の例は、現行の個別製品の仕様・在庫を示すものではなく、層数だけで接合方法や個別製品の硬度は判断できません。同社も複合する材料によって硬度などが変わると注記しています。購入時は層数に加えて、組み合わせる材料と製品固有の仕様を確認するための解説です。