Degummed Silk Yarn: How Raw Silk Becomes Soft and Lustrous
Degummed silk yarn is silk yarn from which the natural gum, called sericin, has been removed. Raw silk naturally contains two main parts: the inner silk fibre, called fibroin, and an outer gummy coating, called sericin. This gum holds the silk filaments together, but it also makes the yarn feel harsh, stiff, and dull.
Before degumming, silk yarn is not as soft and shiny as we usually imagine silk to be. It may feel somewhat hard, wiry, and rough. Its colour may range from white to fawn or yellowish because of the natural gum and impurities present on the fibre surface.
What Is Degumming or Boiling-Off?
The degumming process is also called boiling-off. In this process, thrown silk yarn is boiled in hot water and soap. The soap and heat gradually remove the sericin from the silk. Once this gum is removed, the true nature of silk appears. The yarn becomes soft, flexible, smooth, lustrous, and white or cream in colour.
This is why degummed silk is sometimes called soft silk. The word “soft” here does not only mean soft to touch. It also means that the yarn has been freed from its natural gum and is now suitable for dyeing, weaving, embroidery, and fine fabric production.
The Scroop of Silk
A special feature of silk is its scroop. Scroop is the characteristic rustling or crisp sound produced when silk is rubbed or moved. It is one of the traditional ways people identify real silk.
This sound is not naturally strong in fully degummed silk. It is often developed during dyeing by treating the degummed silk with a dilute acid. The acid treatment gives silk that crisp, lively handle and rustling sound.
Loss of Weight During Degumming
When silk is degummed, it loses weight because a significant portion of the original yarn was made up of gum. The loss is usually around 20 to 25 percent.
For example, if we start with 16 ounces of thrown silk, after boiling-off it may be reduced to about 12 ounces.
This does not mean the silk has been wasted; it means the gum has been removed and the remaining fibre is the finer, purer silk substance.
Why Silk Is Sometimes Weighted After Degumming
However, this loss in weight was often commercially important because silk was sold by weight. To recover the lost weight, silk was sometimes weighted during dyeing. This means substances such as tannic acids or metallic salts were added to the silk. These materials increased the weight of the yarn after degumming.
In some cases, the weight of silk could be increased by 50 percent or more without greatly reducing its natural lustre. The silk would still look bright and attractive, but its actual composition would include added weighting materials. This practice was especially important in the silk trade because it affected cost, handle, durability, and fabric behaviour.
Understanding the Count and Loading of Silk
The count and the loading of silk were often stated together. For example:
Two-thread tram, 30/32 denier, 22/24 oz dye
This expression can be understood in parts.
A tram silk thread is a thrown silk yarn generally used as weft yarn in silk weaving. “Two-thread” means that the yarn is made by combining two raw silk singles. Each single may be approximately 14/16 denier, and when two such singles are thrown together, the total yarn becomes about 30/32 denier.
The phrase 22/24 oz dye refers to the final dyed and weighted condition of the silk. It means that 16 ounces of original silk, after losing about 25 percent of its weight during degumming, has been weighted during dyeing so that the final dyed silk weighs 22 to 24 ounces.
Sequence:
16 oz raw thrown silk → about 12 oz after degumming → 22/24 oz after dyeing and weighting
This shows how the original gum loss could be more than recovered by loading the silk during dyeing.
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In Simple Terms
In simple terms, degumming changes silk from a stiff, dull, gummy yarn into the soft, lustrous, flexible silk yarn we usually associate with luxury fabrics. The process removes natural gum, improves handle and shine, prepares the yarn for dyeing, and reveals the real beauty of silk.
However, because degumming reduces weight, silk was often weighted during dyeing to restore or increase its commercial weight.
