silk is a process that starts with a silk moth (fig.) laying its eggs. When these
hatch, the tiny caterpillars (fig.)
are fed on cut-up
White Mulberry (fig.)
leaves. In about three weeks after hatching they start to
spin their silky cases, called
rang mai dip
in one continuous thread,
by producing silk in two salivary glands in their head, a process that lasts
around 3 days to a week, depending on the silkworm's strain and climate
sericulture, the pupae are usually
placed in a
krajo, a traditional
breeding basket arranged in concentric circles (fig.),
or in a brush-like arrangement of sticks on a string, which in
is known as cao long (草龙), literally a ‘straw dragon’ (fig.).
The silkworm produces the silk as a liquid secretion known as fibroin which is
cemented together with a viscous gum-like substance called sericin. These
substances harden when coming in contact with the air. There are two kinds of
cocoons, depending on the silkworm's gender, i.e. white (to light green) and
yellow cocoons (fig.).
White cocoons are made by the male silkworm, have a long and smooth thread and
are especially used to make crisp, smooth woven silk fabrics, like taffeta,
whereas yellow cocoons are produced by the females and have a shorter thread
which is rather rough. As soon as the cocoons are completed the chrysalises are
killed by heat, in Thailand usually by exposing them to the sun for a couple of
days, but elsewhere, in places with less sun and lower temperatures, they are
either killed in an oven or by boiling them whilst simultaneously unwinding the
cocoons. Anyhow, it should be done before the pupa transforms into a moth, as
the moth will secrete a fluid that dissolves the silk, enabling it to emerge but
thus damaging the cocoon. Some pupae are allowed to undergo the metamorphosis
into moths which are used for further breeding. Each cocoon contains about 900
meters of raw silk thread. But, 48 single filaments of raw silk need to be
combined to form yarn strong enough for weaving and not all raw silk is of
suitable quality. That is to say, each cocoon has three layers which vary
in quality and character: the first layer is known as the outer
floss and makes up about 10% of the cocoon's weight, and although it is formed
of a continuous filament, it is more textured and not always suitable to be reeled; the next part or middle
compact layers of the cocoon, also known as the
shell, has a continuous filament
which is smoother than that of the outer part
and is easily reeled; the next part is the innermost
layer of the cocoon, next to the chrysalis and known as the pelade or inner
pelade, a thin membrane-like layer which cannot be reeled.
As a result, up to 5,500
cocoons may be required to produce just one kilogram of same quality silk.
Therefore, a selection takes place, eliminating damaged or imperfect cocoons (fig.),
such as those with holes, spoiled ones, etc. Raw silk is obtained by boiling the
cocoons in hot water (fig.).
This removes the viscous gum-like sericin, thus releasing the silk filaments.
After brushing the cocoons, to find the outside ends of the filament, the
threads are pulled over a
ready for dyeing and looming (fig.). Once the cocoons are completely unwound, inner
carcasses of dead silk
mai in Thai, are the
leftovers. These pupae are edible and considered a delicacy by some. In China,
they are even sold impaled on skewers at food markets, a street snack known as
zha can yong
The silkworm cocoon pelades have a very low porosity that prevents bacteria and ambient water from destroying the pupa. These can hence also be used for other means, e.g.
in the making of bulletproof vests, for which the pelades are pressed into layers mixed with a resin to create a lightweight bulletproof plate that can be inserted in special police vests, an invention by a team of
University researchers and which can withstand .38 and .22 calibre bullets fired from a distance of three metres. At present, China and Japan are the two main producers of silk, together
annually manufacturing more than half of the world's production.