From Silkworm Egg to Silk Thread: Cocoon, Drying, and Reeling

On a trip to Qom, I once had the opportunity to visit a silkworm farm. On wide shelves lined with mulberry leaves, the sound of countless larvae simultaneously munching on the leaves had a unique, rain-like quality. When the farmer explained, "These little creatures will become the silk for the carpets," it finally connected the image of a Qom carpet with the tiny beings before me.

The luster of Persian carpets, especially silk carpets from Qom, is not solely due to weaving and dyeing techniques. The quality of the thread itself, and the long process from silkworm eggs to cocoons, dried cocoons, and reeling, determine the final carpet's sheen and smoothness. Here, we will trace the entire process of silk thread production, step by step.

Silkworm Eggs — A beginning protected at 25°C

It all begins with an egg smaller than a sesame seed. Silkworms have been bred to live with humans over thousands of years and no longer exist in the wild. Adult moths barely fly or eat, dedicating their short lives to laying the next generation of eggs. A single female lays approximately 300 to 500 eggs.

Silkworm farmers carefully manage these eggs in an environment with a temperature of around 25°C and humidity of about 70%. If the temperature is too high or too low, it affects the timing of hatching and the health of the larvae. Management at the egg stage is the first step directly linked to the quality of the final silk thread.

Mulberry Leaves and Larvae — A month of intensive feeding

Once hatched, the larvae continuously feed on mulberry leaves. While they are only a few millimeters long when born, they grow to about 5 cm in about a month. They molt about four times during this period, and their appetite increases with each molt.

The quality of mulberry leaves also affects the quality of the silk. Soft, fresh leaves must be provided daily at regular times. For farmers, daily mulberry picking and feeding is an unending task.

Cocooning — One thread, 1,000–1,500m long

Fully grown silkworms finally begin to build their "cocoons." They spin a fine silk thread from their mouths, moving their heads in a figure-eight motion to enclose their bodies. Within the cocoon, which takes about 2 to 3 days to complete, the silkworm transforms into a pupa.

The length of the thread that can be reeled from a single cocoon is said to be about 1,000 to 1,500m. It is exceptional for a living creature to produce such a long, continuous single thread.

Drying Cocoons (Kanken) — Preventing moths and preparing thread quality

If cocoons completed by silkworms are left as they are, the pupae inside will eventually turn into moths and break out of the cocoons. If this happens, the precious long single thread will be cut midway, making it impossible to obtain a long, continuous thread.

To prevent this, a process of properly drying the cocoons is necessary. This is called "Kanken" (drying cocoons). The method of drying significantly impacts the quality of the silk thread later on.

Methods of Kanken include traditional natural drying and modern machine drying.

• Natural Drying: In Persia, for centuries, cocoons have been spread out in shady, well-ventilated areas and slowly dried by the arid air of the Persian plateau. This method is still chosen by small-scale workshops.
• Hot Air Drying: Warm air is applied to dry cocoons uniformly while precisely controlling temperature and humidity with machinery. The advantage is that it finishes quickly and evenly.
• Vacuum Drying: A method of drying by controlling moisture in a near-vacuum state. This ensures uniform drying even inside the cocoon.

Properly dried cocoons yield strong threads with fewer breaks, smooth threads of consistent thickness, and threads that retain their natural luster. Conversely, if drying is insufficient or too strong, the threads may become easily broken or lose their sheen. For regions that require fine, uniform threads like Qom, the precision of this drying process is particularly important.

Reeling — Extracting thread from cocoons

Dried cocoons are immersed in warm water to soften the sericin (protein) covering the surface of the silk thread. Next, the end of the thread is found, and threads extracted from multiple cocoons are combined into a single strand and wound. This is the reeling process.

The thread from a single cocoon is too fine to be used as carpet thread as is. Threads from multiple cocoons are combined to create a thread of the desired thickness. Twisting the threads (撚り) determines the strength and luster of the yarn. The strength and number of twists are adjusted according to the intended use of the carpet.

In intricate Qom silk carpets, the delicate work of twisting several very fine threads together is required. If the thickness is not uniform during the reeling stage, uneven density will appear in the finished weave.

Dyeing — Adding color to the thread

After reeling, the white raw silk proceeds to the dyeing process. Natural dyes (indigo, pomegranate, turmeric, madder, walnut, etc.) or synthetic dyes are used to prepare the colors for the loom. Dyeing artisans adjust the dye concentration, temperature, immersion time, and choice of mordants based on their experience.

As shown in the picture, dyed threads are bundled and arranged around the loom in the workshop. It is not uncommon to use 20 or 30 colors in a single carpet, so preparing the threads alone is a considerable process. For more on material selection and the dyeing process, please also refer to Wool and Silk — Which to choose for your first piece.

Number of cocoons required for a 1 square meter carpet

After all these processes, the thread for weaving a carpet is finally ready. So, how many cocoons are needed to weave a 1 square meter Qom silk carpet?

It is estimated that about 400 to 600 cocoons are required. In terms of total thread length, this amounts to about 40 to 60 kilometers. This means that a length of silk thread nearly equivalent to the distance from Tokyo Station to Lake Ashi in Hakone is contained in just one square meter of carpet.

For a living room size of 2 meters x 3 meters, the number of cocoons would be 2,400 to 3,600, and the total thread length would be 240 to 360 kilometers. Considering the quantity of material supporting a single carpet, it becomes a little clearer why the price point is at that level.

From silkworm to carpet — A cumulative effort of unseen work

The luster of Qom silk carpets is not solely born from weaving techniques or dyeing skills. Egg management, mulberry leaf selection, cocoon drying, reeling twists, and dyeing temperature control. In each step, there are specialized experts, and their accumulated judgments finally lead to a single silk thread being placed on the loom.

When you hold a Qom silk carpet in a store, and observe the fineness and uniformity of the threads, and the depth of its luster, please take a moment to recall the long process that originated from a silkworm egg. A single carpet reaches your hands not only through the weaver but also through many others: silkworm farmers, reeler artisans, dyeing artisans, and washing artisans.

For more on the weaving and finishing processes involved in making a carpet, please refer to How Persian carpets are made — From design to finishing. After learning about the thread, we invite you to continue and see how it transforms into a single carpet.