What Is Tensan?

What Is Tensan?

Another kind of silk, raised in the mountains and carrying a quiet light within it.

Tensan, also called yamamayu, is a native wild silkworm of Japan that lives in deciduous mountain forests.
Its cocoons are pale green, and the silk carries a distinctive glow that seems to rise softly from within.

If domestic silkworms are raised close to people, tensan are raised with the atmosphere of the mountains around them.
The leaves they eat, the places they grow, and the character of their cocoons and silk are all different from those of domestic silkworms.

A Silkworm Raised in the Mountains

Tensan feed on the leaves of kunugi oak, nara oak, kashiwa oak, and evergreen oaks.
Unlike domestic silkworms, which are raised under close human care, tensan follow a rhythm that comes only once each year in an environment much closer to nature.

Because of this, the cocoons and silk of tensan seem to hold the mountain light, the wind, and the movement of the seasons within them.

Rearing in the Yamanashi Studio

Tensan are raised in the natural surroundings of Ichikawamisato, Yamanashi.
Kunugi trees are planted, and the eggs are attached to the branches for rearing.

Because tensan rearing once took place in many parts of this region, groves of kunugi trees can still be seen here and there.
That memory of the land continues to support the life of tensan today.

A journal record of tensan rearing is also available.
Read A Year of Silk Raised in the Mountains

The Cycle of Life

Eggs laid in late summer pass through the winter and hatch around the end of April.
The larvae grow for about 55 days, passing through four molts and reaching the fifth instar.

They then spend about two days making their cocoons among the leaves and become pupae.
The cocoon filament is about 600 to 700 meters long. From early August to late October, the moths emerge, mate, and lay eggs, carrying life into the next generation.

The Character of Tensan Silk

Wild silkworm cocoons are much harder to reel into silk than domestic silkworm cocoons.

Tensan silk has a distinctive glow. It is light, soft, and warm because it holds air within the thread itself.
At the same time, it is strong, and it carries a quiet presence unlike that of any other fiber.

Domestic silkworms have long been improved to make reeling silk easier, but wild silkworm cocoons are difficult to reel at all.
That difficulty is also part of the rarity and beauty of tensan silk.

How yamamayu Uses Tensan

Miyasaka Silk Mill | Reeling and winding

Parts that cannot be reeled are hand-spun in the studio.

At yamamayu, not only reeled tensan silk but also the parts that cannot be reeled are carried forward into the work by spinning them in the studio.
The parts that can be drawn long and the parts that cannot both continue into cloth with their own different expressions.