Dyeing and bleaching of wool can be and is carried out at many stages throughout manufacturing. Where it is carried out is dependent upon a number of factors, including effect required, lot sizes, effect on aesthetic qualities, need for quick response and economics.
Although there are exceptions, wool is dyed or bleached at the following stages:
- scoured loose wool: almost exclusively for wool to be processed on the woollen system
- combed top: for long runs for the worsted sector, both knitwear and woven i.e. blacks, navy blues and corporate and uniforms.
- yarn: package or hank for the worsted sector. Hank dyeing is beneficial to yarns for flat-bed knitting, because it tends to increase the bulk and improve the hand feel
- knitted and woven fabric: for quick response
- knitwear: for woolen-spun and worsted-spun, for quick response
- woven garment: to create vintage or wash down effects.
Most dyes for wool are anionic (negatively charged) in their chemical nature, and the rate of dyeing is controlled primarily by controlling both the pH and the rate in the rise in the temperature of the dye bath liquor.
The keys to successful dyeing and bleaching depends upon a combination of achieving as accurately and consistently as possible, the correct shade, uniformity (levelness), meeting the colour fastness requirements, at both the least cost and damage to the environment.