Manufacture, Function and Material of Early Iron Tsuba

 

 

Early iron tsuba share material as well as functional affinities based on quality of

metal, forging techniques, carbon content and presence of impurities.

Tsuba were created to endure battle

conditions and protect the user from grave injury. In this context, it would follow that

one should be able to analyse the product from contemporaneous tsubako and katchushi,

and be able to make informed comparisons of technique, material and possibly even age

and place of manufacture.

 

Many scholars believe that early iron tsuba evoke an emotional response which later (Edo

Period) iron tsuba fail to elicit. The limited decorative features of a tsuba in the Sengoku

period captured the desperate yet hopeful mood of turbulent times, therefore, these tsuba

tend to have a subtle elegance yet deeply expressive quality. Such early tsuba were

utilitarian items, designed for potential use on the battlefield, and thus it reasonable to

assume that their owners placed demands on the tsubako to produce a quality product.

The iron quality, construction and aesthetic all seem to lose functionality, to be replaced
by emphasis on artistic qualities during the
Edo.

 

Material Considerations

Perhaps the two most important and characteristic, and yet most poorly understood

aspects of early tsuba manufacturing techniques are 1) folding of the metal and 2)

heterogeneous carbon distribution. As collectors we look for these features manifested as

fold or weld lines and various forms of tekkotsu (iron bones) respectively. Tekkotsu may
be defined as segregated areas of high carbon content, formed as a result of

a process of successive episodes of heating, folding and hammering of an iron plate.

Generally speaking, increasing the carbon content in iron, results in decreased ductility.

Thus, a localized area of high carbon content (tekkotsu) effectively forms a localized hard

spot. These localized areas of decreased ductility tend to interfere with crack propogation

by deflecting or blunting the crack. These attributes are often used as indicators to distinguish
older and higher quality tsuba, however, many collectors fail to understand just why this is so.

 

From a mechanical perspective, both folding and carbon distribution alter the stress

behavior of the iron tsuba in ways which increase resistance to impact. Folding iron

greatly increases resistance to ballistic and notch-impacts by dissipating the impact

energy from effectively a point or line source to a greater surface area provided through

successive planes of laminated material that tend to shear or delaminate rather than

fracture.

 

The combination of the laminated plate of a tsuba, with heterogeneous carbon is thus a

very effective crack arrestor. Evidence of this is seen in the thinness of the earliest iron

tsuba. Perhaps the tendency to thicken the rim and/or plate of a tsuba toward the end of

the Muromachi period is attributable to attempts to find balance between tsuba integrity

and the call for increasing amounts of artistic design elements via sukashi in a tsuba

meant for the battle field.

 

Another consideration in understanding early iron tsuba is material is the tsuba

composed of high carbon steel or iron, and what are the implications of this distinction?

Kremers (1994) briefly addressed the question of steel vs. iron, pointing out the main

problems as being the difficulty in distinguishing between the materials in an old tsuba,

and in identifying the possible source of the materials employed in the manufacture.

 

The high degree of variance among Muromachi tsuba suggests that a potentially large

number of independent artists scattered throughout the country were responsible for

production. Iron ore extraction in Japan was uncentralized and resource constrained. Old

records indicate that a number of ore deposits were exhausted at various times during the

Muromachi, and resource replacement was a constant issue, especially during times of

civil war when the demand for iron surged. This would suggest that iron qualities varied

regionally as well as through time. It is reasonable to assume that iron

workers across Japan had to purchase raw materials from common sources, and as

Kremers and others have suggested, that they may have been instrumental in avoiding

wastage by re-using scrap materials.

 

The implications are that some tsuba were made as secondary products of early sword

manufacturing shops, while others were made as secondary items by some armor

manufacturers. As usual, modern nomenclature sways us into potentially

erroneous associations. The term kokatchushi tsuba was applied first to early iron tsuba

whose sukashi motifs, robust mimi and iron character reminded people of some late

Muromachi mempo and hachi. The term kotosho was based on observations by some

scholars of metal similarities between certain early iron tsuba and the metal of sword

tangs. Both terms are thus based on subjective observations, and

yet they have been broadly incorporated, and likely over-used.

 

If these terms are reflective of manufacture, then kotosho tsuba

should be made of highly refined iron or steel that was likely folded, and associated with

blade manufacture. Kokatchushi tsuba would then be made from scrap metal used in the

production of armor, which may have been folded, but generally more iron-like in feeling

and appearance.

 

I think the safe and most reasonable approach is to recognize the tremendous variety in

early iron tsuba, and that many groups or independent producers utilizing a wide range of

methods were actively engaged in their production, and often participated with others

with materials and ideas. This participation may well have come from groups

involved in the production of armor or swords, but the actual physical or documented

evidence of such an association is non-existent.

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EDL