brief look at silk
Silk was dug up in 8,500 year old Chinese tombs. In 3630 BC silk fabric was used at the YangShao Neolithic(5000 BCE -3000 BCE) culture site excavated in 1921 in Henan province. Silk was rugged and withstood ravages of time due to material properties. We owe the process of making fabric and the spread of silk throughout the world to two royal Chinese women.
Before the 27thcentury BCE, silk was rare and could only be used by royalty. Then, Empress Leizua legendary Chinese empress discovered sericulture (making silk and rearing silkworms). According to tradition, she also invented the silk loom that propagated silk finery throughout china. A Chinese myth tells one day a silkworm (really a larvae of the moth, Bombyx mori) fell into her tea, and the heat unwrapped the silk around its body until it stretched across her entire garden. When the silk ran out, she saw a small cocoon and realized that this cocoon was the source of the silk. The Emperors of China strove to keep knowledge of sericulture secret. The great demand and explosion of production is owed to a Chinese princess who on a trip on the Silk Road revealed the secret to merchants. From there the strands of the silk story unfold to modern times.
The first image is a silk fiber, 6-10 microns in width. It was produced by the larva when morphing into pupa stage. The larva secretes silk from two glands glued together before drying. The strands produce a flat triangular cross section. Look closely and you can see change in width at twists in the fiber and the reflection shimmering off the fiber. The strands are most evident at the thicker part of twists. The three flat sides reflect light in a semi-refraction pattern which creates the glossy surface of the fiber and fabric. The second image is a cocoon made from a single 1.7 Km long fiber spun by the larva. Notice several broken fibers pulled away. The third image is a cocoon with a newly emerged moth. Silk fiber compares to the best steel in elasticity and tensile strength. Go to link for the material properties. Thanks foldscope. I volunteer teach in the inner city and will incorporate this fun tool into a class project, hopefully on the environment. Comments wanted