Grading
The cotton qualities from place to place and
plant to plant differ the difference in quality can be expressed in grading and
staple length. Grade is generally determined from three factors i.e,
(a)
Colour,
(b)
Trash content and
(c)
Ginning quality
Colour
Best
cotton is only white in colour. But continued exposure to weathering and micro-organisms
cause white cotton to lose its brightness. The colour groups present in cotton
are White,
Light spotted (Lt Sp), Spotted (Sp), Tinged
(Tg), Yellow stained (YS), Light grey (Lt Gy), and Grey (Gy).
Trash Content:
The
trash includes such materials as leaf, stems, hulls. bark, seeds, shale, motes,
grass, sand, oil and dust. Cottons which contain minimum amount of trash after
ginning have highest spinning value. Depending upon the trash content, cotton
can be graded as Strict Good Middling (SGM), Good Middling (GM), Strict
Middling (SM), Middling (M), Strict low middling (SLM), Low middling (LM),
Strict good ordinary (SGO) and Good ordinary (GO).Sometimes, depending upon the
trash content, plus (+) can be given to any grade like SLM+ or SGM+.
Quality of Ginning:
Presence
of neps and naps are two important factors to determine the quality of cotton. Neps
are small tangled knots of fibre that are visible as dots. This type of cotton
is known as neppy cotton. Naps are large clumps or matted masses of fibres that
contribute to the rough appearance. This type of cotton is known as nappy
cotton.
In general, the grading indicates the trash and colour of the
cotton like LM Tg, M Lt Gy etc.
