Degummed Silk Yarn: How Raw Silk Becomes Soft and Lustrous

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.

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.

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Relative Twist of Yarns: Why Finer Yarns Need More Turns Per Inch

Relative Twist of Yarns

Relative twist of yarns means comparing the twist in two yarns in a fair way, even when the yarns are of different thicknesses.

A thicker yarn and a finer yarn cannot be compared simply by saying both have the same number of turns per inch. For example, 12 turns per inch in a thick yarn will not give the same effect as 12 turns per inch in a fine yarn. This is because the fibres in a fine yarn lie on a smaller diameter, while the fibres in a thick yarn lie on a larger diameter. Therefore, the angle at which fibres spiral around the yarn surface becomes important.

The same relative twist is obtained when the angle of twist on the surface of the yarn is the same. In simple words, the fibres in both yarns are inclined at the same angle, even though one yarn is thicker and the other is finer. This gives a similar yarn character in terms of firmness, handle, strength, and appearance.

Formula for Relative Twist

For similar yarns, the relative number of turns per inch is proportional to the square root of the yarn count.

Relative twist ∝ √Count

This means that finer yarns need more turns per inch than coarser yarns to produce the same relative twist.

Example: 16s Yarn and 25s Yarn

For example, compare 16s yarn and 25s yarn.

The square root of 16 is 4.

The square root of 25 is 5.

So the relative twist required is in the ratio:

4 : 5

This means if 16s yarn has 12 turns per inch, then 25s yarn should have proportionately more twist.

12 ÷ 4 = 3

So each unit of relative twist equals 3 turns per inch.

For 25s yarn:

5 × 3 = 15

Therefore, if a 16s yarn has 12 turns per inch, a 25s yarn should have 15 turns per inch to have the same relative twist.

This does not mean that 25s yarn is “more twisted” in character. It means the finer yarn needs more actual turns per inch to create the same twist angle and similar yarn behaviour.

Why Relative Twist Is Useful

This concept is very useful in fabric manufacturing. Suppose a mill is producing the same type of cloth in different weights. A heavier version may use a coarser yarn, while a lighter version may use a finer yarn. To keep the cloth feel, appearance, and performance similar, the yarns should have the same relative twist.

For example, a coarse cotton fabric and a finer cotton fabric may both need a soft, smooth, balanced handle. The yarn counts may differ, but by adjusting the turns per inch according to the square root of the count, the manufacturer can maintain a similar yarn structure.

Limitation of the Rule

However, this rule works best when the yarns are of similar material, similar spinning method, and not extremely different in thickness. If one yarn is very coarse and the other is very fine, many other factors begin to affect the result, such as fibre length, fibre fineness, spinning system, yarn evenness, and intended fabric use.

In Simple Terms

In simple terms, relative twist helps maintain the same yarn character across different yarn counts. A finer yarn needs more turns per inch than a coarser yarn, but when the twist angle remains the same, both yarns behave in a similar way in the fabric.

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Mercerization: The Midas Touch That Makes Cotton Shine

Mercerised cotton yarn is cotton yarn that has been specially treated to make it smoother, stronger, brighter, and more silk-like in appearance. Ordinary cotton yarn has a soft, slightly dull look because cotton fibres are naturally flat, twisted, and ribbon-like. In mercerisation, this natural fibre structure is changed by chemical treatment and controlled stretching.

The process begins by passing the cotton yarn through a cold and strong solution of caustic soda, also known as sodium hydroxide. This solution is quite concentrated. When the cotton yarn comes into contact with it, the fibres swell and the yarn contracts, usually by about 20 percent. This contraction happens because the caustic soda penetrates the cotton fibres and changes their internal structure.

At this stage, the cotton fibres no longer remain flat and twisted like ribbons. They swell, become more rounded, straighter, and more transparent. This change is very important because rounder and smoother fibres reflect light more evenly. That is why mercerised cotton develops a bright, silky lustre.

However, lustre does not develop fully by chemical treatment alone. The yarn must also be stretched. After the yarn contracts in the caustic soda solution, it is stretched back close to its original length. This stretching is done while the yarn is still impregnated with alkali. The tension helps align the fibres and creates the permanent shine associated with mercerised cotton. If the yarn is allowed to shrink freely without being held under tension, the lustre will be much less.

The tension is maintained while the caustic soda is washed out. This is important because the yarn must remain straight and controlled during the removal of alkali. After washing, the yarn is passed through a dilute solution of sulphuric acid. The purpose of this acid bath is to neutralise the remaining caustic soda. Since caustic soda is strongly alkaline, it must be neutralised properly so that it does not damage the yarn later. After neutralisation, the yarn is washed again and then dried.

The best mercerised effect is obtained when the yarn used is already of high quality. Combed yarn gives better results than carded yarn because combing removes short fibres and impurities, leaving longer, smoother, and more uniform fibres. Gassed yarn gives even better lustre because the tiny projecting fibres on the yarn surface are burned off before mercerising, making the yarn surface cleaner and smoother.

Two-fold yarn is often preferred because it is more uniform, stronger, and rounder than single yarn. A slightly lower twist than ordinary two-fold yarn is useful because too much twist can prevent the fibres from swelling evenly and reflecting light properly. High-quality cotton is also important because long, fine, mature fibres respond better to mercerisation.

Earlier, Egyptian cotton was commonly used for mercerised yarn because of its long staple length, fineness, and superior quality. Such cotton produced excellent lustre and strength after mercerisation. Later, improved processing methods made it possible to obtain good mercerised results from better grades of American cotton as well.

In simple terms, mercerisation changes cotton from a soft, dull, ribbon-like fibre into a smoother, rounder, shinier, and more silk-like fibre. The caustic soda causes swelling, the stretching creates lustre, the acid neutralises the alkali, and washing and drying complete the process. The final yarn looks richer, takes dye better, has improved strength, and gives fabrics a more polished and premium appearance.

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Why Combed Cotton is better than Carded Cotton

Why Combed Cotton Is Better Than Carded Cotton.

Cotton yarn may look simple from the outside, but the way cotton is prepared before spinning makes a major difference to the quality of the final fabric. Two commonly discussed types of cotton yarn are combed cotton yarn and carded cotton yarn . Both are made from cotton, but they differ in fibre selection, smoothness, strength, lustre, cost, and final fabric appearance.

Combed Cotton Yarn

Combed cotton yarn is made from cotton that has undergone an extra process called combing after carding.In combing, the cotton fibres are passed through fine combs. These combs remove short fibres, neps, tangled fibres, immature fibres, small impurities, and weak fibre portions.Only the longer, more parallel, and better-quality fibres remain. So, combed yarn is more refined than carded yarn.

Why Is Combed Yarn Cleaner and Smoother?

Because short fibres and impurities are removed, the remaining fibres lie more evenly and parallel to each other. This produces a yarn that is smoother, cleaner, stronger, more even, less hairy, and more lustrous. The yarn surface becomes compact and refined.This is why combed cotton is often used in premium shirts, fine sarees, high-quality bedsheets, innerwear, and luxury knitwear.

Why Is Combed Yarn Stronger?

Long fibres create better grip and continuity in the yarn. When fibres are longer and more parallel, they bind better during twisting. Therefore, combed yarn has better tensile strength, uniformity, abrasion resistance, durability, and pilling resistance. This makes it suitable for finer and higher-quality fabrics.

Why Is Combed Yarn More Lustrous?

Lustre increases when fibres are more parallel. In combed yarn, the fibres reflect light more uniformly because they are better aligned. So the yarn and fabric look slightly more polished, clean, and refined.

Why Does Combed Yarn Have Less Filling Power?

Combed yarn has less filling power because the short fibres are removed. This is important. Short fibres create bulkiness and a fuller appearance. When these short fibres are removed, the yarn becomes smoother and more compact, but less bulky. So combed yarn may feel finer and cleaner, but it may not cover fabric space as fully as carded yarn. In simple words, combed yarn gives smoothness and strength, but carded yarn gives more body and coverage.

Half-Combed, Ordinary-Combed, Super-Combed, and Double-Combed Yarn

There four levels of combing. Half-combed yarn removes about 11 per cent waste and involves mild combing, where some short fibres are removed. Ordinary-combed yarn removes about 15 per cent waste and represents standard combing. Super-combed yarn removes about 18 per cent waste and involves more intensive combing for finer quality. Double-combed yarn removes about 24 per cent waste and represents very intensive combing for premium yarn. The more waste removed, the better the fibre selection. But the cost also increases because a larger portion of cotton is rejected as waste. So double-combed yarn is costlier than ordinary-combed yarn.

Why Is Combing Expensive?

Combing increases cost because it requires additional machinery, slows down production, removes usable fibre as waste, often needs better-quality cotton, and requires more process control. That is why combing is generally used only when the yarn needs to be fine, strong, smooth, and premium.

When Is Combed Yarn Used?

Combed cotton yarn is preferred when fine count yarn is required, high-quality fabric is needed, smooth hand feel is important, lustre is desired, strength is important, and low hairiness is required. Examples include premium shirting, fine voiles, high-count bedsheets, luxury T-shirts, fine cotton sarees, high-quality poplin, premium innerwear, and mercerized cotton fabrics.

Carded Cotton Yarn

Carded cotton yarn is made from cotton that has been carded but not combed. Carding opens, cleans, and roughly aligns the cotton fibres, but it does not remove short fibres as thoroughly as combing. So carded yarn contains more short fibres, more fine impurities, more fibre ends, more hairiness, and more bulk. So it a more fibrous or “oozy” thread. Here, “oozy” means the yarn surface has small protruding fibres, giving it a fuzzy or hairy appearance.

Why Is Carded Yarn Less Smooth?

Because it still contains short fibres. These short fibres do not align as well in the yarn structure. Their ends protrude from the yarn surface, creating hairiness.So carded yarn is less smooth, less even, less lustrous, more hairy, more bulky, and less refined.

Why Cannot Carded Yarn Be Spun to Very Fine Counts?

Fine yarn requires long, uniform, clean fibres. Since carded yarn contains many short fibres and impurities, it becomes difficult to spin into very fine yarn. Short fibres do not hold together well in very fine counts. They increase breakage during spinning. Therefore, carded yarn is more suitable for medium and coarse counts.

Why Is Carded Yarn Cheaper?

Carded yarn is cheaper because it skips the combing process, less fibre is removed as waste, production is faster, machinery cost is lower, and more of the raw cotton is used. So carded yarn is economical.

Why Is Carded Yarn Useful for Well-Covered Cloth?

Carded yarn contains short fibres, so it is bulkier and more hairy. This bulkiness helps the fabric cover the surface better. A fabric made from carded yarn may look fuller and more opaque because the hairy fibres fill the gaps between threads. So carded yarn is preferred when the fabric needs good coverage, fullness, soft bulk, warmth, opacity, and economical production. Examples include denim, flannel, towels, casual cotton fabrics, lower-cost shirting, canvas, bedsheets of medium quality, and hosiery in lower to medium ranges.

Super-Carded Yarn

This is not the same as combed yarn. In super-carded yarn, the cotton is still not fully combed, but it has been specially cleaned. Very short fibres and fine impurities are removed more carefully than in ordinary carded yarn. So super-carded yarn is between carded and combed yarn in quality. It is better than ordinary carded yarn but usually not as refined as combed yarn. Ordinary carded yarn is basic quality. Super-carded yarn is an improved carded yarn. Combed yarn is superior quality. Super-combed or double-combed yarn is premium quality.

Main Difference in Simple Terms

Combed cotton yarn mostly contains long fibers, while carded cotton yarn contains both long and short fibers. In combed cotton yarn, short fiber removal is high, whereas in carded cotton yarn, it is low. Combed cotton yarn has fewer impurities, higher smoothness, better luster, higher strength, less hairiness, less bulk or filling power, better ability to spin fine counts, higher cost, and a clean, smooth, refined fabric appearance. It is best suited for premium and fine fabrics.

Carded cotton yarn has more impurities, lower smoothness, duller luster, lower strength, more hairiness, more bulk or filling power, limited ability to spin fine counts, lower cost, and a fuller, softer, more covered fabric appearance. It is best suited for economical and well-covered fabrics.

Textile Interpretation

The choice between combed and carded yarn is not simply “good versus bad.” It depends on the required fabric. Combed yarn is chosen when the goal is refinement, smoothness, strength, and fine count spinning. Carded yarn is chosen when the goal is economy, bulk, opacity, warmth, and fabric coverage. So the manufacturer selects the yarn based on the final fabric purpose.