Silk

      The official definition of the word silk is “yarn reeled from cocoons spun by caterpillars of silk-producing insects.” Only the domesticated silkworm, 'Bombyx mori' is reared systematically, and it is this variety which accounts for almost all of the world's silk production. Although we commonly refer to the “silkworm”, it is not really a worm, but a caterpillar. The Bombyx mori moth is blind, and although it has wings, is incapable of flight. It also doesn't have a digestive system, and is doomed to die 3 or 4 days after laying its 300-500 eggs.

      Silkworms, having a 30 day growth cycle, will shed their skin four times, grow 8 to 10 centimeters long, and increase their body weight by 10,000 times within this period, feeding exclusively on mulberry leaves. Silkworms are very finicky. They refuse to eat leaves that are too damp, too hot or mixed with any foreign matter. Fifteen grams of silk eggs produce about 30,000 silk worms that will consume over 2,000 Pounds of mulberry leaves. 

      At the end of its cycle, the silkworm will stop eating and raise its head, a sign that it is ready to start spinning the cocoon. Then, with rhythmic movements of its head, it emits through a tiny hole in its lower lip, the silk filament in semi-liquid form which solidifies on contact with the air. In this way, the caterpillar builds up 20 to 30 concentric layers of thread. Gradually, the caterpillar disappears inside its cocoon, which remains porous to enable it to breath. The cocoon spinning lasts approximately 36 hours. If the silkworm remains too long in the cocoon stage it will emerge as a butterfly thereby damaging the cocoon shell. Such cocoons can not be used for reeling into yarn.

      Cocoons in the major silk producing countries are white in color and produce a smooth fine yarn which is more suitable for machine reeling and power loom weaving. Elongated golden-yellow cocoons are traditional Thai cocoons raised throughout the Northeast. The ultimate appearance of hand woven Thai silk is due to the species of silkworms that produced the original cocoon. The 'humps and bumps' coined by legendary silk promoter Jim Thompson, are specific only to Thai silk yarns. In general, the outside layer of the yellow cocoons yield a coarse yarn suitable for weaving thicker quality while the inner part of the cocoon is a lighter weight finer filament.

      In the villages, the unwinding or reeling of cocoons is a slow laborious task typically requiring 10 hours for only 5 kilos of cocoons, just enough to weave 2 meters of silk. The length of the silk filament can reach 1,000 meters for white cocoons and average about 500 meters for the smaller yellow Thai cocoons. Both the yellow and white cocoons must be cooked in boiling water before reeling is possible. The water softens the natural gum )sericin) which tightly binds the continuous filaments together.

      Traditionally, Thai farmers in the Northeast have raised silkworms as a source of additional income. Members of the farmer's household must spend much time tending to their bamboo trays of hungry worms, whose constant chewing has been said to sound like 'the falling of light rain on leaves.' Most of the estimated 400,000 farm families producing silk manage to make only one to two kilos each per year.