“Degummed” on a silk spec tells you how much of the silk’s natural gum has been washed out. That one word changes how the scarf feels, how it hangs, how it takes colour and how it behaves at the seams. This guide explains what the word means, what can go wrong, and what to write into your order.
What the gum is
A silk filament has two parts. The core is a protein called fibroin. Around it sits a second protein, sericin, a sticky gum that holds the strands together. Sericin is not a small coating. It makes up a large share of the weight of raw mulberry silk (Wikipedia: Sericin).
Degumming is the hot, wet process that removes sericin. Soap, alkali, acid and enzymes can all be used (Pant and Bhatt, Banasthali University). Because sericin is heavy, degumming takes away a substantial part of the fibre’s weight. Weight loss is also the simplest way to measure how far degumming has gone (review in Polymers).
The three words you will see on a spec
- Raw, hard or gum-on silk. The sericin is still there. The silk feels firm and a little rough, and it has less shine.
- Partly degummed silk. Some of the gum is removed and some stays. The French trade name is “souple”. It keeps body and a softer, more matte look.
- Degummed, boiled-off or soft silk. Nearly all the gum is removed. It is smooth, soft and lustrous.
These words describe a range, not fixed points. “Partly degummed” from one mill and “partly degummed” from another can feel quite different. That is why the sample matters more than the word.
Hand and drape
Removing the gum changes almost everything a buyer can feel in a scarf, stole or kaftan.
Sericin makes fabric feel harsh and stiff. When it is removed, stiffness drops and the fabric drapes better (Pant and Bhatt). A study of degummed and partly degummed silk fabrics found that removing more sericin lowered the drape coefficient, which means the cloth falls more softly. It also lowered abrasion resistance (Lee, Lee and Yu, Journal of the Korean Society of Clothing and Textiles).
A kaftan or a long stole gains from that soft fall. For a structured scarf, a bow tie or a lining that must hold a shape, some gum left in can help.
Lustre
Gum-on silk looks duller. Once the gum and other impurities are removed, the surface becomes smoother and whiter, with the shine people expect from silk (review in Polymers).
Weight and density
The fibre loses weight. The cloth does not always feel lighter, though. Degumming a woven fabric is a wet process, and wet processing can shrink the fabric. The yarns pack closer, and the cloth can end up thicker and heavier per area than before (Pant and Bhatt). So if you specify fabric weight, say whether you mean before or after degumming.
Strength and creasing
Both sericin and fibroin carry load. Removing the gum lowers tearing strength. The softer fabric also recovers less well from creasing (Pant and Bhatt). Silk is also weaker when wet than when dry (CSJM University course notes). A degummed silk is a finer, softer, more delicate fabric, and it needs to be handled that way in washing and in wear.
Shrinkage and size
Silk that has not been washed can shrink when it gets wet, as the fibre structure relaxes. The same course notes advise pre-washing silk before garment construction (CSJM University course notes). For a buyer, this means one thing: cut and sew only after the last wet process. If a kaftan is cut from gum-on fabric and the gum comes out later, the panels will change size.
Edges and seams
Gum holds yarns in place. Take it out and the yarns move more freely. This follows from the softer, more pliable fabric described above. In practice, check for three things on a degummed sample:
- Cut edges that fray quickly.
- Seams where the yarns pull apart under strain, which shows as a small gap next to the stitching.
- Rolled hems that sit flat and even, without waves.
A gum-on or partly degummed fabric holds a hand-rolled hem crisply. A fully degummed one gives a softer edge that may need a finer needle and a closer stitch.
How degumming fits with dyeing and printing
Sericin blocks dyes and chemicals from getting into the fibre evenly. Degumming improves smoothness, softness and even dye uptake (Pant and Bhatt). Sericin can also take up dye itself, sometimes faster than the fibroin (review in Polymers). But colour held in sericin is less secure. Partly degummed silk fabrics showed poor colour fastness to sweat, because the sericin was not stable under those conditions (Lee, Lee and Yu). For a scarf worn against the neck, that matters.
This gives a simple order of steps:
- Yarn-dyed silk (stripes, checks, woven patterns). The yarn has to be degummed before it is dyed, so the degumming happens at the yarn stage.
- Piece-dyed silk (solid colours dyed after weaving). The fabric can be woven from gum-on yarn and degummed as cloth, then dyed. The shrinkage from that wet step happens to the whole piece, before cutting.
- Printed silk. The fabric is degummed before printing, so the print colour reaches the fibre evenly. Any gum left in patches can show as patches in the print.
Uneven degumming
If gum comes out of one area more than another, those areas take dye differently. The result is streaks, cloudy patches or a shade difference across the width. Yarn construction plays a part. In one study, the warp was almost free of sericin while some sericin stayed on the highly twisted weft (review in Polymers). This matters for twisted constructions such as crepe and georgette, where warp and weft can end up with different amounts of gum.
Over-degumming
Hot, strong alkali used for too long attacks the fibroin core as well as the gum. Strong soda degumming has been reported to cause serious damage to the main fibroin protein chain (Anand, Pandey and Pandey). A silk that feels very soft but tears easily, or looks hazy instead of bright, may be over-degummed.
Chafing and lousiness
Degummed silk resists abrasion less well (Lee, Lee and Yu), and it is weaker when wet. Fabric that rubs against itself or against machinery while wet can pick up chafe marks: pale, rough lines or patches where the surface has been worn.
“Lousiness” is an older term for a visible surface defect on silk cloth. A study from Seoul National University linked it to split ends in the filament and found it was easiest to see in low, raking light along the grain. Plain weave showed less lousiness than twill or satin (Choi and others, Journal of Sericultural and Entomological Science). On a satin scarf, check for it before you approve.
What to write into your silk order
- Degumming state. Write “fully degummed”, “partly degummed” or “gum-on” in words. Do not leave it out and assume.
- Reference sample. Name an approved physical sample for hand, drape and lustre. The word alone is not enough, because “partly degummed” covers a range.
- Stage. Say whether the silk is degummed as yarn or as fabric, and that it must be degummed before dyeing or printing.
- Fabric weight. State whether the weight you quote is before or after degumming.
- Cutting. Ask that all cutting and sewing happen after the last wet process.
- Colour. Ask for an even shade across the width and from piece to piece, with no streaks, and for colour fastness to sweat and washing that suits a garment worn on the skin.
- Surface. Ask for no chafe marks, no fuzz and no hazy patches.
What to check on the sample
- Feel and fall. Hold the scarf by one corner. Compare its drape and softness with your reference.
- Light. Look at the fabric in low light from the side, along the grain. Look for streaks, cloudy areas, fuzz and pale rubbed lines.
- Shade. Fold the fabric so the two selvedges meet and compare the colour edge to centre.
- Wash. Wash a piece the way your customer will. Measure it before and after, and look again at the colour and surface.
- Sweat and rubbing. Rub a damp white cloth on the colour and see whether it stains.
- Strength. Pull gently across a seam and next to a rolled hem. Look for yarns sliding apart. Tug a small cut edge and see how fast it frays.
- Print. On printed silk, check that the colour reaches the back of the fabric evenly and that no patches look paler.
For the wider process from yarn to finished piece, see how a custom silk scarf is made.
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