The Art of Mulberry Silk Production, From Silkworm Cocoon to Fabrics

Silk has captured the hearts of many as a premium, luxurious fabric that seamlessly blends tradition with modern trends. More importantly, silk garments and products offer exceptional comfort and health benefits to the wearer. We owe a huge debt of gratitude to Leizu(嫘祖), the legendary figure credited with its discovery.

Naturally, people are curious about how this exquisite fabric is made. In this article, we’ll take a brief journey through the fascinating process of Mulberry silk production.

What is Mulberry Silk

Silk is a natural protein fiber produced by silkworms as they feed on mulberry leaves. The silkworms spin these fibers into a protective cocoon around themselves. This cocoon is the raw material used to create silk fabric.

To turn these cocoons into beautiful silk fabric, people unwind the long, thin silk threads and weave them together. Let’s delve into the detailed process of silk production, from silkworm rearing to fabric weaving.

Step 1. Mulberry Cultivation and Silkworm Rearing

Silk fabric starts with the cocoons spun by silkworms. To raise silkworms, farmers need to grow mulberry trees, as silkworms feed exclusively on mulberry leaves. Mulberry trees are usually planted a year before silkworm rearing begins to ensure a steady supply of fresh leaves.

The quality of the mulberry leaves plays a vital role in the health of the silkworms and the quality of the silk. Therefore, it’s important to choose the right soil and climate conditions for mulberry cultivation. Regular care, including pruning, fertilizing, and pest control, is essential to maintain healthy mulberry trees and high-quality leaves.

From tiny eggs to silky cocoons, raising silkworms is a fascinating journey. It involves three main steps: hatching, feeding, and spinning. Each step is crucial for producing high-quality silk.

1. Hatching the eggs

Each spring, as temperatures rise and nature awakens, it is the optimal time for silkworm eggs to hatch. To accelerate the hatching process, the eggs can be exposed to sunlight, a traditional practice in China known as “yucan(浴蚕)” .

Newly hatched silkworms are delicate and should be placed on clean white paper before being transferred to a silkworm basket, a traditional and still widely used tool in silkworm rearing. While modern silk farmers may employ more advanced equipment, the bamboo silkworm basket remains a staple in the industry.

2. Feeding the worms

Baby silkworms are very tiny and weak. They need to eat soft and fresh mulberry leaves. As they grow bigger, they can eat tougher leaves. It’s important to keep the leaves dry to prevent the silkworms from getting sick. Modern silkworm farms are very clean and germ-free.

The silkworm, or domesticated silk moth, undergoes four molting stages during its larval phase, resulting in five instars. These molting cycles are crucial for the silkworm to grow and develop.

• First Instar: Upon hatching, the tiny silkworm, often referred to as an “ant silkworm” due to its size, enters its first instar. After approximately 3-4 days, it molts into the second instar.
• Second Instar: Following the first molt, the silkworm enters the second instar and continues to feed and grow for another 3-4 days before molting again.
• Third Instar: After the second molt, the silkworm enters the third instar. This stage, along with the first two, is collectively known in ancient China as the “three sleeps(三眠)” due to the quiescent period before each molt.
• Fourth Instar: The silkworm molts again after about 3-4 days in the third instar, entering the fourth instar.
• Fifth Instar: The final molt marks the beginning of the fifth instar. In this stage, the silkworm experiences significant growth and its appetite increases dramatically. The Chinese term for this final molt is “great rise(大起)” The silkworm’s feeding activity becomes so intense during this stage that it sounds like a gentle rain. After approximately 6-8 days of rapid growth in the fifth instar, the silkworm ceases feeding.

These molting cycles are essential for the silkworm’s growth and development, allowing it to accommodate its increasing size and prepare for the final stage of its life: cocoon spinning.

3. Spinning cocoons

As the silkworm nears the end of its larval stage, it begins the process of cocoon formation. The silkworm’s body shortens and becomes translucent with a golden hue. At this point, the silkworm is carefully transferred to a special frame or rack, a process known as “mounting(上簇).” The frame is often made of bamboo, wood, or other materials and provides a structure for the silkworm to spin its cocoon. Modern silk farms often use specially designed gridded frames that allow for easier handling of the cocoons.

The silkworm spins silk to form a cocoon with a high content of sericin and uneven thickness.

1. The silkworm begins by spinning a loose, irregular layer of silk, known as the outer cocoon layer or floss,
2. Then the silkworm’s body begins to bend into a “C” shape, and its head and thorax move rhythmically, spinning silk in “S” or “8” patterns. This process proceeds from front to back, layering the silk. Once a certain thickness is achieved in one spot, the silkworm shifts to another location and continues, layer by layer, forming silk sheets. These silk sheets are held together by sericin, creating a cocoon layer.
3. In the later stages of cocoon formation, the silkworm’s body significantly shrinks, its head movements slow down and become uncoordinated, and the spinning becomes irregular. The silk gradually contains less sericin and becomes loose, forming a disordered silk layer inside the cocoon, known as the “pupal lining.”

Eventually, the silkworm is completely enclosed within the cocoon, where it will pupate and eventually emerge as a moth.

Step 2. Cocoon Harvesting, Selection, and Boiling

Once the silkworm has spun its cocoon, it’s time to harvest it. This process involves removing the cocoons from their rearing frames, a step known as “dismounting(下簇).” After dismounting, the cocoons need to be degummed to remove the sericin, a sticky protein that binds the silk fibers together. Traditionally, this was done by hand, but modern silk mills use degumming machines for efficiency.

In the past, a process called “cocoon storage” was used to prevent the pupae from prematurely developing into moths. Cocoons were stored in sealed containers to ensure they remained intact and ready for processing.

Historically, cocoons were often stored in sealed containers to prevent the pupae inside from developing into moths too early. This allowed for more controlled processing and ensured the quality of the silk.

Cocooning Sorting and Selection

Cocoons vary in size, shape, color, and quality due to factors such as silkworm genetics, rearing conditions, and handling during harvesting. These include defective cocoons, unreelable cocoons, and “double cocoons” containing two or more silkworm pupae. Even within the same variety of silkworm cocoons, there are variations in size, cocoon shell thickness, and color.

Therefore, it’s essential to sort and grade the cocoons before reeling. The process of selecting cocoons is generally divided into two steps: rough selection and fine selection.

1. Rough Selection: In this step, double cocoons and defective cocoons are separated from the rest. The remaining cocoons are classified as “top-grade cocoons” suitable for silk reeling.
2. Fine Selection: Building on rough selection, this step involves removing substandard cocoons from the top-grade cocoons and sorting the remaining cocoons by shape.
3. Cocoon Sizing: Cocoons are screened for size using a sieve. Smaller cocoons fall through the sieve, while larger ones remain. The sieve gap size can be adjusted according to silk reeling requirements.

Additionally, cocoons with spots or unusual colors should be separated to avoid uneven silk color or mixed fibers.

Boil the Cocoons

Before the silk can be reeled, the cocoons must be cooked in hot water. This process, known as cooking or boiling, softens the sericin, making it easier to unwind the silk fibers. The temperature and duration of cooking are critical factors that affect the quality of the resulting silk.

While most cocoons are processed for silk production, a portion are typically set aside to allow the moths to emerge. These moths mate and lay eggs, continuing the silk production cycle.

Step 3. Silk Reeling (缫丝)

Reeling is the process of extracting raw silk from cocoons. Often, reeling is done simultaneously with the boiling of cocoons. The boiling process softens the cocoons by transferring heat through water, which softens the sericin (the gum-like substance that binds the silk fibers) without damaging the fibers themselves. This allows the silk fibers to be separated and unwound from the cocoon. The process of unwinding and combining several silk filaments into a single thread is called “抽丝剥茧,” a term that has since become a Chinese idiom meaning to solve a mystery or unravel a complex situation.

Modern silk reeling technology has advanced significantly, with most processes now mechanized. Unlike traditional methods where boiling and reeling were often done simultaneously, modern methods involve a three-step boiling process. First, the cocoons are preheated in water around 70℃. Then, they are boiled in water at 100℃ for a specific period. Finally, the cocoons are soaked in 50℃ water before reeling.

The discovery that boiling softens the sericin without damaging the silk fibers was the result of countless experiments and observations by ancient Chinese silk producers. This demonstrates that the discovery of truth often requires a long process of trial and error, and that significant breakthroughs are usually preceded by gradual, incremental advancements.

Silk reeling is a highly intricate process involving numerous steps, such as cocoon mounting, fiber alignment, fiber gathering, twist insertion, reeling, thread replenishment, thread joining, winding, and drying. While a detailed explanation of each step would be beyond the scope of this discussion, a factory visit would provide a comprehensive understanding of the process.

The accompanying image demonstrates the beautiful and lustrous raw silk that is produced.

Step 4. Weaving and Textile Manufacturing

Once the silk is reeled from the cocoons, it needs to be further processed by twisting and winding the threads together to get it ready for spinning into yarn and weaving.

Doubling is a process where raw silk wound onto bobbins is further processed to improve its shape, softness, and remove any short fibers or defects. This process ensures that the silk is of a consistent quality and dryness, ready for further processing. After doubling and twisting, the silk is collectively dried and becomes white raw silk ready for packaging and shipping.

The prepared silk thread is then sent to weaving mills for weaving into fabric. Warp and weft are the two main types of yarns used in weaving. Warp yarns run lengthwise along the fabric, determining the length of the fabric, while weft yarns run crosswise.

The terms warp and weft originate from ancient Chinese astronomy, where they were used to map out the celestial sphere. The application of these terms to fabric reflects the ancient Chinese belief that everything in the universe is connected to nature. Before processing silk, ancient Chinese people would often perform rituals to express gratitude to the ”tiāndì“ and their ancestors for the gift of silk. (“Heaven and earth” does not fully capture the essence of the Chinese concept of 天地 (tiāndì), as it encompasses a much broader and more profound meaning.)

While warp and weft are the primary yarns in weaving, there are many other techniques that can be used to create different types of fabrics. For example, twisting and twill weaving can produce a variety of fabrics. In ancient China, fabrics like silk crepe, gauze, satin, and damask were commonly produced. By adding elastic materials, it was also possible to create stretchy silk fabrics.

Step 5. Dyeing, Embroidery, and Finishing

Silk dyeing can generally be divided into two main methods:

1. Yarn dyeing: Silk yarn is dyed before weaving. This method ensures even color distribution throughout the yarn and allows for better control over dyeing quality and effects. It also provides more flexibility for textile design, as different yarns can be dyed in various colors or patterns to create diverse and intricate fabrics.
2. Piece dyeing: Silk fabric is dyed after weaving. This method, also known as piece dyeing or fabric dyeing, ensures a uniform color throughout the entire fabric and is suitable for mass production. It also allows for more complex and detailed pattern designs on the fabric.

Beyond these two common methods, there are also specialized dyeing and weaving techniques such as plant dyeing, hand dyeing, and jacquard weaving.

In addition to dyeing, silk fabrics can be further embellished through processes like embroidery and jacquard weaving, which are similar to those used for other types of fabrics.

Silk Applications

Silk, renowned for its luxurious feel, durability, and natural beauty, finds a wide range of applications in the textile industry: Apparel, Sleepwear, Bed linens, Hair Accessories, Home decor, and more. From everyday wear to high-end fashion, silk’s versatility makes it a sought-after material.

Look for more information on the applications of silk in this article: The Allure of Mulberry Silk: Where Tradition Meets Trend – Sufabrics

Summary

The journey from silkworm to silk fabric is a complex and intricate process. From sericulture to weaving, each stage requires meticulous attention to detail. The result is a luxurious and versatile textile that has been prized for centuries.

Silk production is more than just a manufacturing process; it is a cultural heritage. Rooted in ancient traditions, the production of silk has evolved over centuries, resulting in a wide variety of fabrics with unique qualities and characteristics.