Page 28 - Curriculum Visions Dynamic Book

given out slowly, so although wool is slow to feel damp, it is also slow to dry out. On the other hand, slow drying means that woollen garments when worn wet do not cause chilling to the skin, as would be the case for quick-drying materials such as cotton.
Wool can be stretched during manufacture and hold this longer shape. However, when washed,
it shrinks back to its original length. That is why woollens tend to shrink on first washing. Wool is easily harmed by high-temperature washing and is food for certain moths. It is not very resistant to mildew.
The natural matting of wool, so carefully avoided during clothes washing, can be encouraged in
a process called felting. Felt is used for pool
tables, tennis balls, felt-tipped pens, and hats.
Silk
Silk is a filament from
cocoons produced by the caterpillars known as silkworms.
(Left) Felt still has a range of special uses, including hats and felt-tipped pens.
(Above and above right) Silk moth cocoons are placed in tubs of hot water to soften the gluelike substance that covers the silk filaments. The filaments can then be drawn off to make threads.
Silkworms raised by people
are allowed to go through their larval
stage (silkworm) and then pupate (create
a cocoon for themselves by spinning a silk
thread). The silk they release is a continuous filament. Two filaments are produced, each of a protein called fibrin. The silkworm also puts out a glue called sericin, which binds the filaments together.
In the natural life cycle of the silkworm the adult moth emerges by breaking open the cocoon. People don’t want this since it breaks the filament, and so the pupae are killed inside their cocoons using steam.
The cocoon is placed in hot water, which softens the glue and allows the filament to be unwound. A single cocoon can produce a continuous filament nearly a kilometre long.
Several cocoons are unwound at the same time, making a twisted strand of raw silk. Strands are combined until a yarn of usable thickness is produced.
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