Silkworms Almost Ready to Make Cocoons

It takes an average of 27 days from the day the one millimeter baby silkworms hatch until they make cocoons. They sleep and shed their skins four times. So there are five eating periods between the sleeps.  In this time their body mass grows 10 000 times. They eat almost constantly if they have a very fresh supply of leaves. The day before they start spinning cocoons their appetite drops dramatically and they eat only 30% of what they ate the previous day. Today they look like they will burst they are so full and healthy. Tomorrow afternoon their inside chemistry will change all the food they have eaten and stored into a liquid silk. They will shrink in size and then start to crawl out of the trays and look for a place to make cocoons. Then they spit out the liquid through two holes in their mouths. Two silk fibers and a coating of glue (sericin) that will bind the two silk fibers together and give body to the thread to give the cocoon  some firmness so it won't collapse.

This is important information because that glue remains even when made into thread. It makes up approximately 10% of the weight of the thread and it should be removed to some degree. When it is removed the silk becomes shiny and softer and somewhat weaker. This is not always desirable. All this shine. It depends how you want to use the silk.

The amount of the glue removed effects the threads absorption and reflection of natural dyes. I prefer to just remove less than half. If you are going to dye something a very light color it is better to de-gum the silk more as the glue proteins with eventually yellow and muddy your colors.

The glue can be removed with an alkali bath or with enzymes that eat up the glue and leave the thread fibers. There are de-gumming solutions on the market. In old days rice straw was burned and used to make an alkali bath. I prefer to only remove part of the glue as I don't want a shiny soft silk thread but a firmer slightly lustrous one. I often get told that , "It doesn't look like silk." There are so many ways to make silk thread and combine and twist these threads that the result is often not a shiny very fine thread and resulting material.

Here is a snapshot of three kinds of thread I made from cocoons. The lightest pink fluffy one is spun silk. I removed 100% of the glue in an alkali bath. After boiling the cocoons for an hour until there is only the fiber left all matted like wool. I remove the chrysalis of the silk moth and then spin the floss like you would cotton or wool. It is soft and light.

The second shiny pink thread has been de-gummed after I reeled it into thread. It is soft and shiny. The darker red color silk has only been de-gummed in boiling water. All three came from the same variety of cocoon and were dyed with madder.  Perhaps only one fifth of the amount of glue was removed in the darker red thread, almost all of the glue was removed form the middle one.  The only slightly de-gummed green thread below was dyed with gardenia pods and then dipped in the indigo a few times. For me, this kind of understated luster is easier to use.

De-gumming the silk to the desired degree has been an issue with silk use since the beginning of silk use thousands of years ago. Complicating matters slightly is the fact that different breeds of silkworms contain a different percentage of the glue and some kinds of silkworms make a very tough glue. Some of the silk varieties in Laos were so tough that removing the glue with an alkali bath, no matter how gently done, would damage the thread to some degree. I brought a few kilograms of this kind of silk to the Tokyo Metropolitan Fiber research center and experimented using enzymes to remove the glue at different percentages. The results were interesting. The different softness's achieved and the later different natural dye absorption levels. 

I usually use a commercially available low temperature de-gumming agent on the silk I make. I use the minimum amount recommended at the lowest temperature and shortest recommended time. (This stuff is precious and keeping it as close to original form is important.) It is wise to de-gum the full amount of silk you will be using for one project as it is impossible to get the same results twice. The color absorption will not be the same twice. Contrary to popular belief the less glue removed, the deeper and easier the silk is to dye. There is some confusion with the idea that fabric and thread need to be de-gummed and cleaned before they will dye. This is true for removing the glues and sizing used on woven cloth before dyeing. It is not true for thread that has been reeled from cocoons. It is desirable to remove some glue to get a softer thread but not all of it.