An egg-shaped casing of silk spun by the silkworm round itself to protect itself in its dormant stage as a pupa (chrysalis). It produces a viscose fluid made up of fibroin and a gum called sericin, together, from two sets of glands along its body. This it emits through an orifice, called a spinneret, in its head and it hardens on contact with the air to form a filament. With this it spins, layer after layer, in a figure-8 pattern round itself, forming its cocoon. This is the source of silk.
Cocoons are graded.
- Good cocoons: perfect for mechanical reeling.
- Pointed cocoons – (found rarely) not good for mechanical reeling.
- Extra large cocoons called cocalons (in French).
- Duppioni: double cocoons.
- Loose, transparent cocoons called soufflon (in French).
- Perforated or pierced cocoons.
- Cocoons containing dead chrysalis
- Rotten cocoons.
- Cocoons with petrified or calcinated chrysalis.