Setting of Wool Fibres in Dyeing

The degree of permanence of set (to release in boiling water) in single wool fibres which have been dyed whilst held stretched, varies widely with the method of dyeing. Dyeing under neutral to slightly alkaline conditions and dyeing by afterchrome methods produce high degrees of permanent set, but supercontraction can occur after the use of strongly acid or acid chrome-mordant methods with sexivalent chromium. All dyeing processes give temporary set, but this can be much less with certain processes carried out at low temperature or under strongly acid conditions. The steaming of tufts of fibres, previously dyed (or chrome-dyed) by different methods under tension, produces marked differences in length and crimp. Twist is set more completely than extension and is less affected by subsequent steaming.