Masterpiece
National Treasure
Collection: Fujita Art Museum
Height: 6.4–6.8 cm
Mouth diameter: 12.3 cm
Outer diameter of footring: 3.8 cm
Height of footring: 0.4 cm
The clay, like that of other Tenmoku tea bowls from the Ken-gama kiln, is a dense, iron-colored clay. Perhaps due to the rapid turning on the potter’s wheel, the surface is smooth, and years of handling have even given it a dull luster. Naturally, the clay is visible only in the small areas of the foot and the side of the foot, as is customary; the rest is entirely covered in glaze, and the rim is encircled by a silver-colored rim.
The glaze, which is the lifeblood of this tea bowl, can be described simply as a vitreous, deep black glaze.
However, it is not uniformly so; subtle variations in color and luster appear depending on where the glaze is thick or thin. Let us first examine the interior. Near the rim, the glaze is inevitably thin, so it reflects the underlying clay color, resulting in a black that is somewhat reddish-brown; everywhere else, it is a deep black.
If you examine this deep black glazed surface closely, you will notice that it is dotted with numerous small specks. This is the origin of Yōhen. If you view it without shining light at too much of an angle—that is, so that the glazed surface does not scatter the light—you will see many small, dull silver-gray rings floating on the surface. And within these rings, black dots become visible to the eye. However, when oblique light is shone upon them, these dull-colored rings emit a brilliant radiance of ultramarine and deep purple. The mysteriously glowing yōhen, therefore, is not the black dots themselves, but rather the rings surrounding them.
Yet, upon closer observation, one notices that while the blue glow is most pronounced within these rings, it also extends to the surrounding areas. As mentioned in the overview, the phenomenon of yōhen is caused by an extremely thin film that forms on the glaze surface.
When oblique light strikes this film, complex diffuse reflection occurs, resulting in the yōhen effect; this effect is particularly strong in the ring-shaped area mentioned earlier. Conversely, within the black spot at the center of the ring, for some reason, the film produces almost no diffuse reflection. Consequently, the blue light surrounding the black spots shines brilliantly across the glaze surface, much like the corona of a solar eclipse.
Looking at the bird’s-eye view of the interior, there is a spot in the upper left where the blue light radiates in a rabbit-hair pattern. This occurs because the black spot did not remain a single point but left a trail as it flowed downward; as a result, the surrounding blue light was cut off by the rabbit-hair pattern, causing this phenomenon. These black spots or streaks can be considered akin to oil droplets and the ripples they create. They interfere with the diffuse reflection of the glaze, producing the ring-shaped or rippled blue light. Moreover, in this tea bowl, the degree of diffuse reflection from the glaze is exceptionally strong, and the iridescence takes on an extreme bluish hue, at times giving the impression of a “U-no-madara” glaze. It is only under such exceptionally favorable conditions that this glaze effect could be achieved, and it is by no means without reason that this piece is counted among the top one or two of the five surviving Yo-hen Tenmoku bowls in the world. The exterior appears to have been subject to slightly less favorable conditions than the interior; the iridescence of the glaze is less pronounced, and the yohen effect is subdued. However, since this is the only known example in which the yohen effect appears on the exterior as well, it must be highly prized as a treasure of the world.
Renowned since ancient times as a great treasure, this tea bowl was passed from Tokugawa Ieyasu to Mito Mitsukuni and was handed down through the generations of the Mito Tokugawa family. However, during an auction held by the family in the Taisho era, it passed to the Fujita family. It is said that the original Tenmoku stand was separated from the bowl at that time.
(Masahiko Sato)
