Contamination in cotton bales is checked in three stages: manual sorting of a sample from each bale lot, inspection of samples in the mill's fibre laboratory, and in-line sensors on the blowroom and carding machines that detect and eject foreign matter during processing. Indian cotton has a reputation for higher contamination than machine-picked cotton from some other origins, mainly because it is hand-picked and handled in sacks and open yards. The problem is well known, so good ginners and spinners have built routines to manage it, and a buyer can ask for evidence of each stage.
The contaminants that cause the most trouble are polypropylene strands from woven sacks, jute fibres from packing, human and animal hair, coloured threads and cloth scraps, and occasionally leaf, seed coat and sand. Polypropylene is the worst because it does not take dye, so it appears as white specks in a finished fabric and is often only found after dyeing.
Checks at the ginner
The first line of defence is at the ginning stage, where seed cotton arrives from farms. Reputable ginners in Saurashtra and Kutch pay for cleaner picking, insist on cotton bags rather than polypropylene sacks, sort cotton on tables before ginning, and keep yards and conveyors covered. Bales from a ginner that does none of these things will carry contamination into every later stage, no matter how good the spinner is.
Checks at the spinner
- Manual sorting: workers open a sample of bales from each lot, spread the cotton on tables under good light and pick out visible foreign matter, recording the weight and type found per bale.
- Laboratory grading: the fibre lab assesses contamination alongside length, strength, micronaire and trash, and assigns the lot to a mixing accordingly.
- In-line detection: optical and ultraviolet sensors on the blowroom line identify foreign fibres and coloured contaminants and blow them out of the stream.
- Yarn clearing: contaminants that survive to the yarn are cut out by clearers on the winding machines, which also log the number of foreign fibre cuts per unit length.
- Fabric inspection: for sensitive end uses, the mill knits a sample from the lot and inspects it before and after dyeing.
What to ask for as a buyer
Ask the spinner for its contamination report for the lot you are buying, which should show the manual sorting results and the foreign fibre cut rate from the clearers. Agree a contamination grade in the purchase order, specify that bales must arrive in cotton packing rather than polypropylene, and state the end use so the mill knows how sensitive the fabric will be. A knitted and dyed sample from the actual lot, inspected under daylight, is the single most useful check before you approve shipment.
If your fabric is white or pale, or if it will be dyed in a light shade, ask for a mixing from contamination-sorted cotton even if it costs a little more. Reprocessing a dyed fabric with polypropylene specks is far more expensive than a cleaner mixing.
How Creston & Co helps
We visit ginners and spinners, look at the sorting tables and the clearer logs ourselves, and send sealed lot samples to an NABL-accredited lab so contamination and quality are checked independently. We supervise loading and send weekly updates while your order is in production. A free 20-minute sourcing review is the easiest way to find out whether your current supplier's contamination controls are up to standard.