Fabric defect · Dyeing and printing - Uneven dyeing in fabric: streaks, patches and their causes

Uneven dyeing is color that is not the same all through the cloth. It shows as streaks, blotches or specks. The cause can lie in the fiber, the yarn, the way the fabric was woven or knitted, its preparation, or the dyeing itself, and the shape of the fault is often the first clue.

Uneven color in a strip of fabric: soft patches lighter and darker than the rest, and a faint streak.

What uneven dyeing is

A U.S. federal glossary of fabric imperfections defines uneven shade, or uneven dyeing, in one line: "Color is not uniform throughout the cloth." It lists a dye streak as "a dye stain extended as an irregular stripe in the cloth," and mottled cloth as having "a blotchy or spotted appearance" ¹.

Cotton Incorporated uses mottled for "a condition where color or dye is unevenly applied to or accepted by a fabric" ². The dye can go on unevenly, or the fiber can take it up unevenly.

Dyeing can turn unlevel when the fiber takes up dye from the bath too fast, so dyers add retarding, or leveling, agents to slow it down ³.

What causes uneven dyeing

Some causes start before the fabric reaches the dyehouse: in the fiber, the yarn, or the way it was woven or knitted ⁴. Others start in preparation or in the dyeing itself ⁵.

What causes uneven dyeing
Stage	What happens	What to check
Fiber	Poor blending of cotton in yarn manufacturing can lead to poor dyeing uniformity in the yarn or the fabric ⁴.	Cotton blending
Yarn	Yarn generally over a year old, woven or knitted with new yarn, does not dye the same as the new yarn ⁴. A yarn of different dye affinity mixed in while creeling the warp shows as a line ².	Yarn age and lots, and creeling
Weaving and knitting	Differences in yarn tension, yarn abrasion, high and low twist yarns mixed together, or yarns of different luster give dyeing defects in straight lines ⁴.	Yarn tension, twist and luster
Desizing	Size not fully removed, from processing too fast, no desizing agent, or a bath hot enough to destroy the enzymes, can leave warp streaks and uneven dye penetration ⁵.	Desizing time, agent and temperature
Scouring	Incomplete scouring gives blotchy goods and poor dye penetration, and can leave loom oils in the cloth ⁵.	Scouring, and oils used at the loom
Mercerizing	Uneven mercerizing makes goods streaky when they are dyed, because the cotton takes up dye at different rates ⁵.	Even mercerizing
Drying and heat setting	Folds left on a relaxation dryer can hold moisture and dye unevenly ⁶. In cotton and spandex, top layers and edges that dry while the goods wait heat-set differently, which gives uneven dyeing ⁷.	Fabric spread flat, and even moisture before heat setting
Dyeing	Dye taken up too fast gives unlevel dyeing ³. Poor dye penetration can make goods blotchy or streaky, and a careless choice of dyes can give a specky look as open yarns take up more of one color ⁵.	Dyeing rate, leveling agents and dye selection
Dyeing blends	Poor color matching between the fibers of a spun blend gives a two-tone effect ⁵.	Dyes matched to each fiber
Handling	Chafe or rub marks from rough machine parts can dye darker ⁵. Flat goods such as satins, taffetas and twills need open-width handling "to avoid streaks and creases" ⁵.	Rough machine parts, and open-width handling
After dyeing	Knots dry last and can wick dye from around them, leaving halos, and fabric left wet in a roll turns blotchy as the color migrates ².	Drying, and goods dry before rolling

Where uneven dyeing shows

The shape of the fault is a clue, not proof. Cotton Incorporated's rule of thumb: "if dyeing streaks or unevenness is in straight lines, then the cause of the problem is fiber or yarn related." Tension, abrasion, twist and luster faults from weaving or knitting also show in straight lines ⁴. Wet processing can leave straight streaks too: Goldberg traces warp streaks to size left in the cloth ⁵.

Rubbing damage can hint at when it happened. At times it dyes darker if it came before dyeing, and shows lighter if it came after ⁵. In one of Goldberg's cases, oil that scouring missed left dark sections about 4 inches wide along each selvedge ⁵.

How evenness is judged

When color is judged by eye, the viewing matters. Color matches start to look closer the longer you look, "usually after 15-20 seconds of viewing," and shade booths normally have a standard gray interior to limit the effect of the surround ⁴.

AATCC EP9 sets out how to assess color difference by eye ⁸. Cotton Incorporated notes that it covers lighting, viewing and reporting, and gives no definite pass or fail tolerances for shade matching ⁴.

Instruments measure color; people judge how it looks. Cotton Incorporated strongly recommends using both together. Instruments can struggle with plaids, prints, and textured or surface finished fabrics ⁴.

A dye streak that runs on along the roll is a running defect. One buyer manual, which follows the 4-point system of ASTM D5430, gives up to 4 points to each linear yard or metre in which a continuous running defect exceeds 9 inches, and no linear yard gets more than 4 points ⁹.

What research says

Cotton Incorporated has conducted research showing that differences in micronaire can lead to noticeable color differences in dyed fabric ⁴.

Mercerized cotton appears to dye deeper and brighter than untreated cotton ⁴. Goldberg traces streaks in dyed cotton goods to uneven mercerizing, because the cotton takes up dye at different rates ⁵.

Sources

Pilot - How a pilot starts

We start with recorded video of your inspection frame and agree with your team on one fabric to test. The pilot runs for a set time, and before it starts we agree on what counts as success. For each defect it marks, ConductVision saves a still image and its place on the roll on your network for your inspector to check.

You bring: Recorded video of fabric running over your inspection frame
We set up: One fabric, and the limit you grade it against
You get: Marked defects, running points and a final points forecast for each roll, and a results report checked against what we agreed

Plan a pilot