Cotton dyeing

Dyeing The most commonly used processes for imparting color to cotton are piece dyeing and yarn dyeing. In piece dyeing, which is used primarily for fabrics that are to be a solid color, a continuous length of dry cloth is passed full-width through a trough of hot dye solution. The cloth then goes between padded rollers that squeeze in the color evenly and removes the excess liquid. In one variation of this basic method, the fabric, in a rope-like coil, is processed on a reel that passes in and out of a dye beck or vat. Yarn dyeing, which occurs before the cloth is woven or knitted, is used to produce gingham checks, plaids, woven stripes and other special effects. Blue dyed warp yarns, for example, are combined with white filling yarns in denim construction. One of the most commonly used yarn dyeing methods is package dyeing. In this system, yarn is wound on perforated cylinders or packages and placed on vertical spindles in a round dyeing machine. Dye solution is forced alternately from the outside of the packages inward and from the inside out under pressure. Computers are used increasingly in dyeing processes to formulate and match colors with greater speed and accuracy.