How is Silk Fabric Made

The highest quality silk fabric is produced using commercially cultivated silkworms raised exclusively for silk production. This process is referred to as sericulture. The most desired silkworms are the larva or the caterpillars of the Asiatic mulberry moth Bombyx Mori which feeds on leaves from the mulberry tree. The specialized diet of mulberry leaves creates employment for thousands of workers. The mulberry trees must be cared for, the leaves plucked, chopped and fed to the young larvae every few hours. The trees are then pruned and prepared for the next season’s crop. Chemicals cannot be used on the mulberry trees or the sensitive silkworms will perish. Every 7 pounds of silk requires approximately 1,000 pounds of mulberry leaves. The Japanese have developed a food substitute by mixing mulberry leaves, soybeans and agar. This increases production and reduces labor costs. During the silkworms 25 to 28-day lifespan, they will molt four times as a result of their bodyweight increasing by as much as 10,000 times. After the final molting the silkworms ultimately produce a silk cocoon consisting primarily of two different types of protein - fibroin (70 to 80%) and sericin (20 to 30%).

When a silk cocoon produced by the most commercially desirable Bombyx Mori silkworm is unwound or reeled a continuous cocoon thread referred to as a bave is produced. Some of the largest cocoons can yield a bave or cocoon thread as long as 1,300 yards or .74 miles, approximately 1,200 meters or 1.2 kilometers! To produce 1 pound of silk requires 1,000 miles of cocoon thread from 2,000 to 3,000 average sized cocoons. The bave is not a perfectly round thread, but instead has a cross section resembling a triangle. The single cocoon thread is too thin to be used on its own and must be "thrown" or combined with many other threads to produce a silk yarn thick enough for the weaving process, and many yarns are used to weave the silk fabric. Once woven, silk fabric consists of thousands of small triangular threads. These small triangular threads reflect light like snow on a sunny day, or a diamond with many facets. This is why pure silk fabric has a look and feel unequaled by anything made with manufactured fibers.

There are over 500 species of wild silkworms, which feast on oak and other leaves, and are capable of fending for themselves. The tussah worm is considerably larger than the commercially cultivated variety, sometimes growing to six inches in length, producing an egg-sized cocoon. China produces approximately 80% of the world’s tussah silk. The Assam Valley in India produces a golden colored tussah that cannot be reeled off of the cocoon as with other silks, but instead must be spun like cotton or wool.

Wild silk such as tussah has a very different look because the cocoon thread or bave has a different cross sectional shape, more like a wedge rather than a triangle. The wedge shape of the tussah bave reflects light differently and provides tussah fabric with a unique look. Wild silks such as tussah are not as highly prized as silk made from the mulberry leaf eating Bombyx Mori. This is because the threads are not uniform in color and texture, and because the cocoons of the wild silkworms are not as easily unwound or reeled as a result of being covered with a layer of naturally occurring minerals. Even after de-mineralizing the cocoons that are intact, many of the cocoons used in the manufacturing process have been broken open by the moth resulting in the thrown threads being made out of many short pieces. The end result is a fabric that is not very strong with many more surface irregularities, compared to silk fabric produced using threads from the cultivated Bombyx Mori. Additionally wild silks such as tussah are more difficult to dye since the threads are not uniform in color.

Since silk is a natural fiber, minor surface irregularities are to be expected during the weaving process, which explains why many fabrics such as dupioni and shantung feature what are known as slubs. These small surface irregularities, when kept within reasonable limits, are considered desirable as they signify the authenticity of silk rather than being defects. Similarly, sueded silks undergo special treatments to achieve their distinctive appearance, characterized by gentle shading and slight creases, which should also not be regarded as flaws but rather as enhancements that contribute to the luxurious quality of fine silk fabric.

Even though silk comprises of a mere 0.2% of the world's total production of textile fibers, it will continue to be a sought after luxurious fabric for the discriminating individual. As the New York based designer Oscar de la Renta has said, "Silk does for the body what diamonds do for the hand."