Making Silk

How is silk processed?  Or rather, how did the processing of silk come to be?  I know the legend, but what part of that is truth, and what part is pure myth?  In all likelihood we will never truly know, being that time travel remains in the realm of science fiction.  So lets explore how silk is cultivated today instead.

First up in the process is raising the silkworms.  Bombyx mori is the species used for cultivated silk, but truly, there are many species which produce silk, and not just moths: bees, wasps, ants, silverfish, mayflies, thrips, leafhoppers, beetles, lacewings, fleas, flies, and midges, not to mention many species of spiders, all produce silk.[1]  While the Bombyx mori initially was as wild as the rest of them, thousands of years of selective animal husbandry has left them almost entirely dependent on humans, as their life cycle, already very short, is marked by breeding, laying eggs, and dying shortly after, with no flight in between; all that in breeding has left the moths incapable of flight.  The Bombyx mori is fed a diet exclusively consisting of mulberry, and when the worms (really the moth pupae) are all eating, it can sound like a heavy rainfall on a tin roof.  While in this stage, the pupae eat and poop constantly…just like babies.  At their largest, the pupae reach a length of almost 2 inches.  At the end of 4 weeks, the pupae are ready to cocoon themselves, and are moved to special trays which make harvesting them easy.

Harvesting the silk involves killing the cocooned bug, either by dipping it in boiling water, or piercing the cocoon with a needle.  Then the unreeling can begin.  What was it about the Bombyx mori that made THIS the species of choice when silk began to be cultivated? Probably the ease with which the threads are unreeled.  While still held together by fibroin and sericin, for whatever reason, this cocoon unreels quicker than other bug cocoons.  While the other silks can be unwound, the process of cracking through the protein shells damages the filaments, often producing inferior silks.  Note:  This is changing as advances in technology have allowed for new demineralization processes that allow for stripping the protein shell while leaving the filaments undamaged, which is exciting news in the world of silk, if almost a decade old at this posting[2]

Steps three through five are universal to textile production.  Step three can as easily be pushed to the end, depending on what the end product will look like.  Step three is dying the silk filaments; however, if the end piece is to be all one color, it’s just as likely that the silk is woven natural color, then dip dyed after the fact.  Step four is spinning the filaments in to the thread which is then woven in to the fabric in step five. 

So those are the steps needed to cultivate silk today.  Next week, we’ll explore how this process might have been discovered, by design or by accident, 8500 years ago.

[1] Sutherland TD, Young JH, Weisman S, Hayashi CY, Merritt DJ (2010). "Insect silk: one name, many materials". Annual Review of Entomology55: 171–88. doi:10.1146/annurev-ento-112408-085401PMID 19728833