Source: In common use
Tsuba is written 鍔 or 鐔 in Japanese. Both characters describe the discoid sword guards favored by the Japanese.
Other meanings of the word are the brim of a kettle, hat, or the visor of a helmet.
The Japanese sword is made so that its hilt can be easily disassembled by the removal of a single pin, called the mekugi (目釘). Once removed, the entire hilt comes off and tsuba and grips can be easily interchanged. Expensive swords thus often had a number of sets of sword mountings called koshirae (拵え).
"Sword mountings played an important part in the training of the Japanese of the highest classes. They formed a part of his daily life, they were frequently changed, and wealthy men are said to have had sufficient "stock" in reserve to allow favorite swords to appear in different dress each day in the year." 2
-Bashford Dean, 1921.
(Founder of the Metropolitan Museum Arms & Armor Department.)
Because of this interchangeability, there was -and is- a lively trade in Japanese sword parts, most notably tsuba which are collected as an art form on their own.
A short overview of the most basic parts of the tsuba.
1. Mimi (耳), the rim.
2. Hira (平), the surface.
3. Seppa-dai (切羽台), washer-seat.
4. Kozuka hitsu-ana; (小柄櫃孔 / 小柄櫃穴); aperture to accept the kozuka, the handle of the kogatana.
5. Kōgai-hitsu-ana (笄櫃孔 / 笄櫃穴); aperture to accept the kōgai, a pin-like accessory. Note the slightly different shape.
6. Nakago ana (中心孔 / 中心孔穴); aperture to accept the sword tang.
The seppa-dai or washer seat is usually seen in the form of an oval outline, following the cross-section of the sword's hilt. To ensure a good fit, a spacer or washer, called seppa (切羽), would be placed on either side of the tsuba. The seppa-dai is not always present, but if present, usually left undercorated because this area would be covered by the seppa anyway.
Exceptions to this general rule are some presentation tsuba, imported sword guards from other countries like China, and Japanese copies and interpretations of such guards known as nanban tsuba.
Most tsuba will have at least one of these, but some are entirely without. We also see instances of two kozuka hitsu-ana or two kōgai-hitsu-ana. On some tsuba, the openings fell out of use and were subsequently plugged with a soft metal, often shakudō (a copper-gold alloy that was patinated to a "raven black"), but pure gold, silver or lead are also encountered.
Viewed from the facing side, which is the side where the hilt is, the kōgai-hitsu-ana would usually be situated on the right, with the kozuka hitsu-ana on the left.
The style and workmanship of the hitsu-ana differed per school. The Yagami school for example customarily lined them with sheet metal.
A Yagami "hundred monkeys' tsuba.
Signed by Noda Mitsuhiro II (active circa 1770-1823)
Walters Art Museum, accession number 51.133.
The opening for the sword tang indicates intended use. Most tsuba were made for the large katana or smaller wakizashi which were worn thrust through the belt, edge up. For this reason, the nakago ana is aligned so the edge points upwards in relation to any decoration, if present.
Development and schools
The earliest known tsuba are the so-called tôran-kai (倒卵形) or "inverted egg shaped" tsuba that date from the Kofun period of circa 300-568 A.D. These were most likely made by sword makers themselves.
A tôran-kai tsuba.
Metropolitan Museum, accession number 06.310.9.
The classic aoi-gata (葵形) or hollyhock tsuba emerged in the Heian period of 794-1185 A.D. and remained in use on tachi throughout history.
Classic aoi-gata style tsuba. This one made of foreign steel (nanban-tetsu).
Sold by Mandarin Mansion in 2019.
By the Kamakura period of 1185–1333 A.D., different styles of tsuba were made by mirror makers, sword makers, and armorers. Schools of specialized tsuba makers started to emerge around the Muromachi period of 1336-1573 A.D.
A simple tsuba in the kō-toshō (swordsmith's) style. 14th century.
Metropolitan Museum, accession number 2005.430.
A tsuba in the armorer's style. Signed Nobuiye (circa 1504–1554).
He was part of the famous Myōchin clan of armorers.
Metropolitan Museum, accession number 17.208.65.
Up until this time tsuba were still mostly very sturdy and functional, with modest decoration, if any. The unification of Japan under Tokugawa rule ushered the start of the Edo period, which brought peace and prosperity. Many more schools and branches emerged, making a wide diversity of styles. The most complex and ornate tsuba ever made date from this period.
An Edo period tsuba in soft metals, decorated with a design of peony and butterflies.
Signed Omori Hidenaga (late 18th century), son of the famous Omori Teruhide.
Metropolitan Museum, accession number: 2004.461.
Japanese arms and armor is a vast area of study, with thousands of publications of which I have only read a tiny fraction.
If one has to start somewhere, I'd recommend the Tosogu Classroom series by Markus Sesko. 5 volumes are planned, of which two are published at the time of wrting. They are a translation of the articles of notable expert Fukushi Shigeo which he wrote in the last 30 years for "Token Bijutsu", the NBTHK publication.
On the subject of Japanese sword mountings, and their history see Markus Sesko; Koshirae-Taikan.
Other books I enjoyed were Henry L. Joly; Japanese Sword-Mounts, a descriptive catalogue of the Collection of J.C. Hawkshaw, Esp.,M.A., Of Hollycombe, Liphook. London, 1910. And Helen Cowen Gunsaulus; Japanese Sword Mounts in the Collections of the Field Museum. Field Museum of Natural History, Chicago, 1923.