There are many reasons for white spots to appear during dyeing, such as water spots in the dyeing primer and the reduction steamer. Whiter water spots are closer to the front, while lighter ones are closer to the back. Rounder water spots are caused by areas with a small height difference in the fabric path or by splashing. Longer water spots are caused by areas with a large height difference in the fabric path.

Some white spots can be caused by woven bag strips on the mercerizing machine's paving wheel, which can cause white spots during dyeing. Also, dark spots can be caused by cotton wool on the paving wheel, which can cause dark spots during dyeing. Other causes of white spots include wax spots, alkali mud, and rotten cotton spots.

Fabric Quality Management

Good quality greige fabric will have a high dye uptake, good dye depth, and a smooth, even, and full-bodied surface. Poor quality greige fabric will have severe white spots and unevenness during dyeing. Therefore, when dealing with greige fabrics containing a high concentration of dead cotton, the pretreatment process should be strengthened. While ensuring safe and reliable production, the cotton impurities should be removed as thoroughly as possible, and the dead cotton should be thoroughly cooked to improve dye uptake and dyed fabric quality.

Cold-batch pretreatment of fabrics is now being used by many companies due to its energy-saving benefits. However, cold-batch pretreatment is ineffective in removing cotton impurities and sizing agents, resulting in stiffening of the fabric, which can lead to wrinkles during dyeing. Furthermore, the cloth guide rollers are easily contaminated, resulting in stains and color spots. Therefore, during dyeing, the addition of thickening agents such as anti-migration agents and brightener NT-2 should be minimized.

Treatment of Thick Fabrics 

When producing thick fabrics such as polyester-cotton brushed fabrics or pure cotton, if the scouring process is ineffective and the lint is not thoroughly cleaned, some fine lint can adhere to the fabric surface, making it difficult to remove after being rolled over by the padder. This can result in white spots during dyeing. Some white spots may not be noticeable after dyeing, but if the fabric surface is rubbed in the opposite direction by hand, the lint will fall away, revealing numerous white spots. Some fine cotton wool can be extremely difficult to remove from the fabric, often difficult to detect even after dyeing. However, when adding thickening agents such as anti-wrinkle agents, rain repellents, and cross-linking agents during tentering, the wool can be removed, revealing white spots.

Therefore, white spots caused by cotton wool should not be underestimated. When producing brushed products, it is important to frequently clean the brush rollers on the brushing machine to prevent the wool from adhering to the fabric and becoming difficult to remove after being crushed by the cloth-discharging rollers. If the wool remains after double-cleaning, brush it again with the brush roller on the brushing machine. This will remove the wool before dyeing.

Treatment of Poor-Quality Fabrics

For fabrics with high levels of impurities and dead cotton, increasing the alkali concentration (220g/L) during mercerizing can effectively improve the quality of dyed fabric and reduce white spots and surface irregularities.

During the post-sanding production phase, brushed fabrics must be extremely careful about aurora marks. Once aurora marks appear, they can cause white spots during dyeing. Therefore, during mercerizing and alkali washing after sanding, the padder and fabric guide rollers must be free of any hard objects. Frequent inspections should be performed. If aurora marks are detected during dyeing, they should be treated before dyeing.

This has been encountered during the dyeing of polyester-cotton brushed fabric (two-bath disperse/reactive dye process). White spots discovered during disperse dyeing were not taken seriously enough, and only addressed when the spots became severe during reactive dyeing. To treat aurora marks on brushed fabric, the only way to achieve this is to sacrifice the sanding effect. Using a higher alkali concentration before mercerizing will ensure that the surface feel of the fabric outside the aurora marks is the same as that of the aurora marks. This will eliminate the white spots caused by the aurora marks.