The term horimono (literally "carved things") is used to indicate any work carved on the blade of a Japanese sword, regardless of whether it is a katana, a wakizashi or a tanto.
The purposes of a horimono are essentially four:
The horimono aimed at lightening the blade are generally found on katanas and not on shorter swords. They are called bo-hi and are long grooves obtained with large chisels through the entire length of the blade, on both sides, removing material from the shinogi-ji. There are numerous variations depending on their position, the shape of the end, where they start (inside the tang or visible) and where they end (before the tip or inside it). There are also double hi and others accompanied by smaller incisions.
An interesting feature of many swords of the Nanbokuchō era (1336-1392): in this period full of clashes between samurai clans, the swordsmiths began to make katanas that could be restored in case the tip broke. For this reason the kissaki (tip) is very often long and the hi terminates before it. In fact, if it were necessary to reshape the tip, the hi would remain out of it and would not weaken it.
Votive horimono are religious or auspicious engravings that were meant to protect the samurai and at the same time decorate and personalize his sword. They are more common on small blades, particularly on tanto, and can represent various motifs. Among the most frequent:
The decorative horimono were introduced during the Edo period on the katanas and are generally larger than the votive ones. They often depict a dragon, taking up traditional iconography but using superfine techniques to embellish the blade.
The horimono were finally used even when the steel showed a defect, for example micro-bubbles of air that were revealed only during polishing. A carving made it possible to remove the defective part and bring a top quality to the sword.