All About Silk: What I Learned About Silk Yarn, Knitting and Everything Else

I started researching silk because my knitting grew. I wanted to understand why a garment knitted in silk could look one way on the needles, another way after blocking, and then change again once it had been worn for a while. It was a fairly ordinary knitting question, but five YouTube episodes later I had somehow researched protein structures, ancient China, the Silk Roads, spider farming, samurai armour, surgical sutures, parachutes, silkworm goddesses, mermaids and international caterpillar espionage.

All because I wanted to know why my knitting grows.

That is probably the best explanation for why I enjoy these deep dives so much. A ball of yarn can seem completely ordinary until you start asking where it came from, how it behaves and why humans have spent thousands of years doing increasingly strange things with it.

Now that All About Silk is finished, I wanted to put the most interesting parts of that research in one place.

What Actually Is Silk?

The silk most knitters encounter comes from the domesticated mulberry silkworm, Bombyx mori. Despite the name, a silkworm is not actually a worm but the larval stage of a moth, and humans have been breeding and raising it for thousands of years.

The caterpillars feed on mulberry leaves before spinning a cocoon around themselves. That cocoon is mainly made from two proteins: fibroin, which forms the structural silk filaments, and sericin, which helps bind them together. During textile processing, much of the sericin can be removed in a process called degumming.

What makes silk particularly interesting from a knitting point of view is that the fibre can be produced as an extremely long continuous filament. That is quite different from wool, where shorter staple fibres are spun together to make yarn, and it helps explain why silk can behave so differently depending on how it is processed.

A smooth filament silk can be glossy, fluid and almost liquid in appearance, while spun silk, bourette silk or silk noil can be much more matte, textured and rustic. They may all be silk, but they do not produce the same fabric and they certainly do not behave the same way on the needles.

That was one of the first useful things I learned: silk does not really have one personality. Yarn construction matters just as much as fibre content.

Why Does Silk Grow in Knitting?

This was the question that started the whole series.

Silk is very strong, but strength is not the same thing as elasticity. Wool, especially something springy like merino wool, has natural crimp and a tendency to recover after being stretched. Silk has much less of that bounce, so when it is used in a large, heavy or very drapey garment, gravity can have a noticeable effect.

The stitches can lengthen, the fabric can relax and the whole garment can become longer over time. That is the “growth” knitters often talk about with silk, and it is why a silk sweater can behave very differently from a wool sweater even when both are knitted to exactly the same gauge.

This is also why I do not think gauge tells the whole story. Two yarns can both produce 20 stitches per 10 centimetres and still create completely different fabrics. One might be light, elastic and structured, while the other is heavy, fluid and far more willing to stretch under its own weight.

For silk garments, I want to know what happens to a swatch after washing and blocking, but I also want to know what happens when it hangs vertically. If I am knitting something large, I would much rather let the swatch reveal any bad behaviour before I commit to the whole garment.

Gauge tells you whether the stitches are the right size. It does not tell you whether you are making the same fabric.

Blocking Silk

Silk can change noticeably after washing and blocking, particularly in lace or loose, open fabrics. The stitches relax, the drape becomes more obvious and the fabric may grow, especially if the yarn is already heavy and fluid.

A wet silk garment can also be surprisingly heavy, so I would be cautious about letting it hang under its own weight while drying. Supporting the fabric and testing the yarn first is much safer than assuming that all silk behaves in the same way.

That is really the recurring theme here. “Silk” on a yarn label tells you something, but not enough. A smooth filament silk, silk noil, a wool-silk blend and a mohair-silk lace yarn can all contain silk while producing very different knitted fabrics.

How Silk Became an Industry

Once I had a better idea of what silk was doing in my knitting, I made the mistake of asking where it all came from.

Silk is most closely associated with ancient China, where Bombyx mori was domesticated and sericulture developed into a highly organised form of production. Humans were not simply collecting cocoons. Mulberry trees had to be cultivated, silkworms had to be raised and fed, temperature and timing had to be controlled, cocoons had to be harvested, and the fibres then had to be reeled, prepared and eventually woven.

At some point during the research I started joking that perhaps we did not domesticate the silkworm. Perhaps the silkworm domesticated us.

What is clear is that silk quickly became much more than a fibre. It became an industry, and one valuable enough for knowledge about its production to become wrapped in legends about secrecy and theft.

Silk eventually moved across the huge network of trade routes we now call the Silk Roads, although there was never one single route running neatly from China to Rome. Goods, technologies, religions and ideas moved through a shifting web of land and sea connections over centuries, and silk was only one part of that exchange.

Even the name “Silk Road” is modern, which means nobody in the ancient world was standing next to a camel welcoming people to it. I find that slightly disappointing.

The Legendary Silk Heists

Some of the best stories from the series involve the supposed theft of silk production itself.

One tells of a princess travelling to Khotan who hid silkworm eggs and mulberry seeds in her headdress so that silk could be produced in her new home. Another famous story describes silkworm eggs being smuggled into the Byzantine Empire.

Whether these events happened exactly as later accounts describe is much less clear, but the stories make sense when you think about what silk production actually required. Possessing silk cloth was one thing. Knowing how to produce it was something else entirely.

You needed the silkworm, the mulberry tree, the knowledge of how to raise the insects, the timing of the cocoon harvest and the skills needed to turn the fibre into thread and cloth. In other words, you were not stealing a caterpillar. You were stealing an industry.

And Then There Were Spiders

This is where the research became less restrained.

Silkworms are not the only animals that produce silk. Spiders do too, and spider silk has extraordinary mechanical properties, which naturally leads to the question of why we do not simply farm spiders.

The short answer is that spiders are not especially cooperative livestock. Many are territorial and predatory, which makes large-scale farming much more difficult than raising silkworms.

One of my favourite objects from the whole series is the golden spider-silk textile created in Madagascar by Simon Peers and Nicholas Godley. The silk was collected from more than a million female golden orb-weaver spiders. More than a million spiders!

Suddenly knitting the second sleeve does not seem so bad.

A little Arly Knits P.S.

If this enormous silk rabbit hole has made you want to stop reading about fibres and actually knit something, my Arly Knits catalogue sale is still running for another three days!

And the Pumpkin Vine Wrap you’ve seen me wearing in the Silk finale is also an Arly Knits design. I’m working on getting the pattern ready for release and I’ll share more when it’s ready. No ETA just yet.